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In amniote embryos, skeletal muscles in the trunk are derived from epithelial dermomyotomes, the ventral margin of which extends ventrally to form body wall muscles. At limb levels, ventral dermomyotomes also generate limb-muscle precursors, an Lbx1-positive cell population that originates from the dermomyotome and migrates distally into the limb bud. In elasmobranchs, however, muscles in the paired fins were believed to be formed by direct somitic extension, a developmental pattern used by the amniote body wall muscles. Here we re-examined the development of pectoral fin muscles in catsharks, Scyliorhinus, and found that chondrichthyan fin muscles are indeed formed from Lbx-positive muscle precursors. Furthermore, these precursors originate from the ventral edge of the dermomyotome, the rest of which extends towards the ventral midline to form body wall muscles. Therefore, the Lbx1-positive, de-epithelialized appendicular muscle precursors appear to have been established in the body plan before the divergence of Chondrichthyes and Osteichthyes.

Regular scale patterning, restricted to the caudalmost tail and organized into two opposing rows on each side of the tail, is observed in few chondrichthyans. These evenly spaced scales, in dorsal and ventral rows, develop in an iterative sequence from the caudal tip, either side of the notochord. They are subsequently lost as a scattered pattern of placoid scales develops on the body and fins. An identical organized pattern is observed in tail scales of Scyliorhinus canicula (catshark), where the expression of sonic hedgehog signal is restricted to the epithelium of developing scales and remains localized to the scale pocket. Regulation of iterative scale position by sonic hedgehog is deeply conserved in vertebrate phylogeny. These scales also reveal an archaic histological structure of a dentine type found in the oldest known shark scales from the Ordovician and Silurian. This combination of regulated pattern and ancient dentine occurs only in the tail, representing the primary scalation. Scattered body scales in elasmobranchs such as S. canicula originate secondarily from differently regulated development, one with typical orthodentine around a central pulp cavity. These observations emphasize the modular nature of chondrichthyan scale development and illustrate previously undetected variation as an atavism in extant chondrichthyan dentine.

Understanding the evolutionary emergence and subsequent diversification of the vertebrate skeleton requires a comprehensive view of the diverse skeletal cell types found in distinct developmental contexts, tissues, and species. To date, our knowledge of the molecular nature of the shark calcified extracellular matrix, and its relationships with osteichthyan skeletal tissues, remain scarce. Here, based on specific combinations of expression patterns of the Col1a1, Col1a2, and Col2a1 fibrillar collagen genes, we compare the molecular footprint of endoskeletal elements from the chondrichthyan Scyliorhinus canicula and the tetrapod Xenopus tropicalis. We find that, depending on the anatomical location, Scyliorhinus skeletal calcification is associated to cell types expressing different subsets of fibrillar collagen genes, such as high levels of Col1a1 and Col1a2 in the neural arches, high levels of Col2a1 in the tesserae, or associated to a drastic Col2a1 downregulation in the centrum. We detect low Col2a1 levels in Xenopus osteoblasts, thereby revealing that the osteoblastic expression of this gene was significantly reduced in the tetrapod lineage. Finally, we uncover a striking parallel, from a molecular and histological perspective, between the vertebral cartilage calcification of both species and discuss the evolutionary origin of endochondral ossification.

Monociliated surface cells were found for the first time in an elasmobranch and were common on embryos of Scyliorhinus canicula. They occurred mainly near the anterior end, until Ballard stage 30, but disappeared soon thereafter. The functions of surface ciliated cells suggested in other embryos (e.g. surface currents in lungfishes and amphibians, and determination of left right patterns in amniotes) seem unlikely in elasmobranchs.

Submitted by Boris Flegr (boris@uerj.br) on 2020-11-08T19:05:07Z No. of bitstreams: 1 Karla_Soares.pdf: 3365800 bytes, checksum: 59d2121d3d4a7bea599de3793a7e0e89 (MD5) Made available in DSpace on 2020-11-08T19:05:07Z (GMT). No. of bitstreams: 1 Karla_Soares.pdf: 3365800 bytes, checksum: 59d2121d3d4a7bea599de3793a7e0e89 (MD5) Previous issue date: 2014-02-25 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior The family Scyliorhinidae forms the largest group of sharks with at least 16 genera and 160 species. Known as catsharks, their representatives are characterized by having a slender body shorter than the caudal region, with the first dorsal fin over or behind the pelvic fin, characteristically elongated eyes and triangular pectoral fins, parallel to the body. Belonging to this family, the genus Scyliorhinus includes 16 species presenting a varied and widely used coloration patterns in taxonomic studies. Such patterns have generated problems as species identification, especially for the two species recognized for the Western South Atlantic, Scyliorhinus haeckelii and S. besnardi, considered here as belonging to the haeckelii/besnardi group. This study reviewed to revise the taxonomy of the genus Scyliorhinus haeckelii/besnardi group through a comparative study of external and skeletal anatomy, including morphometric and meristic features in order to clarify the morphological distinction of species, suggesting possible synonyms and describing new species. The specimens analyzed were obtained off Rio de Janeiro to Rio Grande do Sul states, all deposited in the ichthyological collection of the Universidade do Estado do Rio de Janeiro (UERJ). The laboratory work included literature review, identifying the color patterns, preservation, biometrics, statistical analyzes, anatomical preparation, description and production of diagrams and photographs, addressing the most relevant structures. The results obtained allowed the description of the general pattern of the genus Scyliorhinus of the Western South Atlantic, on the basis of the external morphology, coloration, dermal denticles, skulls, jaws, teeth, gill arches, fins and claspers. Specimens classified in the 'haeckelii' and 'besnardi' color pattern had no morphological and statistics differences. In this study, it were also found two other different patterns besides the haeckelii/ besnardi pattern, here called "negrinho" and "intermediate", considered new species and described here as Scyliorhinus sp. 1 and S. sp. 2. According to these results, the species S. besnardi is here considered a synonym of S. haeckelii, as the latter was the first to be described. An identification key to the species of Scyliorhinus of the Western South Atlantic is provided in the present study. It is concluded that more detailed anatomical and taxonomic studies on the other species of the genus Scyliorhinus are needed to better understand the relationships among its members and expansion of knowledge about the biology of these sharks A família Scyliorhinidae forma o grupo mais numeroso de tubarões com pelo menos 16 gêneros e 160 espécies. Chamados de cações-gato, seus representantes são caracterizados por apresentar corpo delgado e menor que a região caudal, com a primeira nadadeira dorsal acima ou posterior das pélvicas, olhos caracteristicamente alongados e nadadeiras peitorais triangulares, paralelas ao corpo. Pertencente a esta família, o gênero Scyliorhinus possui 16 espécies com padrões de coloração variados e muito utilizados em estudos taxonômicos. Tais padrões têm gerado problemas quanto à identificação das espécies, especialmente para as duas espécies reconhecidas para o Atlântico Sul Ocidental, Scyliorhinus haeckelii e S. besnardi, consideradas aqui como pertencentes ao grupo haeckelii/besnardi. Este estudo pretendeu revisar a taxonomia do gênero Scyliorhinus grupo haeckelii/besnardi, através de um estudo comparativo minucioso da anatomia externa e esquelética, incluindo aspectos morfométricos e merísticos, a fim de esclarecer a distinção morfológica das espécies, propondo sinonímias e descrevendo possíveis novas espécies. Os exemplares analisados foram obtidos através de coletas efetuadas desde o estado do Rio de Janeiro até o estado do Rio Grande do Sul, todos depositados na coleção ictiológica da Universidade do Estado do Rio de Janeiro (UERJ). Os trabalhos de laboratório incluíram levantamento bibliográfico, identificação dos padrões de coloração, preservação, biometria, análises estatísticas, preparação anatômica, descrição e produção de esquemas e fotografias, abordando as estruturas mais relevantes. Os resultados obtidos permitiram a realização da descrição do padrão geral do gênero Scyliorhinus do Atlântico Sul Ocidental, considerando a morfologia externa, coloração, dentículos dérmicos, crânios, maxilas, dentes, arcos branquiais, nadadeiras e clásperes. Espécimes classificados nos padrões de coloração haeckelii e besnardi não apresentaram diferenças, morfológicas e estatísticas, que sustentassem a separação em duas espécies. Neste estudo, foram encontrados também dois outros padrões diferentes do padrão haeckelii/besnardi, aqui denominados negrinho e intermediário , consideradas novas espécies identificadas e descritas aqui como Scyliorhinus sp. 1 e S. sp. 2. De acordo com tais resultados, a espécie S. besnardi é aqui considerada uma sinonímia de S. haeckelii, visto que esta última foi a primeira a ser descrita. Uma chave de identificação para as espécies de Scyliorhinus do Atlântico Sul Ocidental é fornecida no presente estudo. Conclui-se que estudos anatômicos e taxonômicos mais detalhados sobre as demais espécies do gênero Scyliorhinus são necessários para melhor compreensão das relações entre seus membros e ampliação do conhecimento sobre a biologia destes tubarões

The distribution and morphology of GFAP-immunoreactive cells was investigated in two elasmobranch species, Scyliorhinus canicula and Torpedo marmorata, in an attempt to distinguish between Horstmann's (1954) hypothesis that the presence of cells resembling mammalian astrocytes is a function of the thickness of the ventricular walls, and Cajal's (1911) hypothesis that astrocytes are a phylogenetic novelty found only in birds and mammals. Two types of GFAP-reactive elements were observed, but the distribution of these differed markedly between the two species. In Scyliorhinus, radial glial cells were predominant and astrocytes relatively rare. In Torpedo, on the other hand, a species in which the ventricles are atrophied and the ventricular walls extremely thick, the overwhelming majority of GFAP-labelled structures strongly resembled astrocytes; occasionally, GFAP-positive cells were observed in the ependyma of the spinal cord. These findings, together with previous results obtained by others in hagfish, provide strong evidence in favour of Horstmann's hypothesis.

Small, intermediate and large-sized embryos of the dogfish Scyliorhinus canicula utilize different ventilatory methods; small and intermediate embryos rely on body movement alone to stir either the jelly or sea water in the capsule, large embryos use conventional pharyngeal pumping to pump water through the case. The effects of environmental changes in O2 tension (0.5–100% air saturation) and temperature (6–18°C) upon ventilatory mechanisms in the developing embryo in situ were studied using non-invasive ultrasonography. All three embryo classes increased ventilation rate with rising temperature: for small embryos, y=2.02x+3.295 (P

Photoperiod has no effect on the growth of embryonic dogfish. Conversely, developmental rates are highly susceptible to temperature variation. Embryos maintained at 16°C grew faster and ecloded earlier than those maintained at 10°C. Increased temperature had no effect on size at eclosion.

A survey of skeletal muscles throughout craniates shows basic kinds of myosin filament arrangement, simple-lattice and superlattice, within the A-band of each sarcomere. Distribution of simple- and superlattice arrangements across a phylogeny of craniates suggests that the superlattice arrangement is primitive and that Amia and teleosts are derived in showing simple-lattice arrangements. Two taxa examined (Scyliorhinus and Acipenser) show both lattice types within the same organism implying that there is not a simple evolutionary transformation of one to the other fiber arrangement. We discuss the possible functional significance of the different lattice types. We believe that the crossbridges may have greater competition for actin binding sites in simple-lattice muscles compared to the superlattice types. © 1996 Wiley-Liss, Inc.

By observing numerous living eggs from the lesser spotted dogfish Scyliorhinus canicula (L.) caught near Roscoff (France) and reared at recorded temperatures as they developed from first cleavage to hatching, the first reasonably complete developmental table was worked out for this classical material in vertebrate embryology. The successive stages, described and numbered from 1 to 34, correct and replace the incomplete stages A–Q proposed by Balfour (J.Anat. Physiol., 10:555–576,1876) and other even less complete series later published, and is unique in the inclusion of a timetable at 16°C. The stages can be identified, usually through the cleared eggshell wall, with naked eye or low magnification. This table of normal stages of Scyliorhinus can be adapted with slight modification to other chondrichthyan fishes. © 1993 Wiley-Liss, Inc.

Scanning electron microscopy of corroded resin casts of the renal vasculature of Scyliorhinus caniculus has revealed a novel vascular pathway arising from the afferent arteriole and bypassing the glomerulus. This glomerulus bypass shunt occurred in 36% of the glomerular casts examined. The shunt ran to join a peritubular network of capillaries and thereby offers the potential to vary the degree of glomerular perfusion and control the proportion of active glomeruli. In 29% of glomeruli two efferent arterioles drained the capillary knot. Glomeruli were located close to the dorsal margin of the posterior mass of the kidney, and towards the lateral edge of the anterior lobes of the kidney of female dogfish. In male dogfish, glomeruli were evenly distributed through the posterior mass of kidney, while in female dogfish 89% of glomeruli occurred in the posterior mass and 11% of glomeruli were located within the small anterior lobes.

Coronary artery anatomy was studied in 16 shark species belonging to 9 families of the orders Hexanchiformes, Squaliformes, and Carcharhiniformes. The study included 101 specimens and used an injection-corrosion technique that obtained internal casts of the main trunks and coronary arterial branches. The results showed 2 main patterns of coronary arterial arrangement: the dorsoventral coronary trunk pattern, shared by lamnoid and advanced carcharhinoid sharks, and the lateral coronary trunk pattern, shown by hexanchoid and squaloid sharks. Scyliorhinus and Galeus had intermediate arrangements of their vessels.

A new catshark,Scyliorhinus tokubee sp. nov., is described based on specimens from the coast of Shirahama, eastern Izu Peninsula, southern Japan. The present species is distinguished from other congeners in having a particular coloration with dark saddles, blotches and numerous small light spots, a wide oral cleft, the anterior nasal flap not reaching the oral cleft, a short interspace between the dorsal fins, developed clasper hooks, and some meristic characters (number of vertebrae, jaw teeth, and spiral valve turns). This species has been bred under captivity for several years in Shimoda Floating Aquarium.

The rostral cartilages of batoid fishes were examined to elucidate their development, morphology and homology. Comparison of a variety of rostral cartilages among elasmobranchs with other groups of vertebrates shows that rostral cartilages originate embryologically from the trabecula and/or lamina orbitonasalis. Because different morphogenetic patterns of the derivatives of the two embryonic cartilages give rise to a wide variety of forms of rostral cartilages even within elasmobranchs, and because morphogenesis involves complex interactions among participating structures in the ethmo-orbital area, we put forward conceptual and empirical discussions to elucidate the homology of the rostral cartilages in batoid fishes. With six assumptions given in this study and based on recent discussions of biological and historical homology, our discussions centre on: (1) recognition of complex interactions of participating biological entities in development and evolution; (2) elucidation of a set of interacting biological and evolutionary factors to define a given morphological structure; (3) assessment of causal explanations for similarities or differences between homologous structures by determining genetic, epigenetic and evolutionary factors. Examples of conceptual approaches are given to make the approaches testable. Although a paucity of knowledge of rostral cartilage formation is the major obstacle to thorough analysis of the conceptual framework, several tentative conclusions are made on the homology of rostral cartilages that will hopefully attract more research on development and evolution in vertebrate morphology. These are: (1) the rostral cartilage in each group of vertebrates examined can be defined by both developmentally associated and adult structural attributes, yet such data do not allow us to assess homology of a variety of forms of rostral cartilages at higher taxonomic categories; (2) the entire rostral cartilage in elasmobranchs is formed by the contribution of the embryonic trabecula and lamina orbitonasalis. The status of the development and homology of the rostral cartilage in holocephalans remains uncertain; (3) there is no simple picture of evolution of rostral cartilages among three putative monophyletic assemblages of elasmobranchs, galeomorphs, squaloids (possibly plus Squatina, Chlamydoselachus and hexanchoids as the orbitostylic group) and batoid fishes. It is highly likely that rostral cartilages in each subgroup or subgroups of these assemblages may be of phylogenetic significance but that it may not serve as a basis to unite these assemblages into much higher assemblages; (4) the tripodal rostral cartilage is unique in form in the group including some carcharhinoid and lamnoid sharks. The status of the analogous tripodal cartilage in some squaloids remains uncertain. The unfused tripodal cartilage of the electric ray Narke is interpreted as developmentally equivalent to, but not homologous with, the unfused or fused ones in the sharks; (5) the rostral cartilage in the electric ray Torpedo is uniquely formed because of its embryonic origin solely from the ventro-medial part of the lamina orbitonasalis, but it is regarded as homologous with the rostral cartilages which are formed by the trabecula and other components of the lamina orbitonasalis in other batoid fishes; (6) the cornu trabecula contributes to the formation of the ventral stem of the rostral cartilage at least in elasmobranchs, especially to a particular set of rostral cartilages, i.e. the tripodal rostral cartilage in the shark Scyliorhinus and dorso-ventrally flattened rostral shaft in the narcinidid electric rays; (7) there is a unique form of a rostral shaft with rostral appendix in skates and probably guitarfishes; (8) there is no rostral cartilage in adult benthic stingrays, pelagic stingrays Dasyatis violacea and Myliobatidae, although it is present in embryonic stages; (9) there is a unique form of the rostral cartilage as a rostral projection from the dorso-lateral part of the lamina orbitonasalis in pelagic stingrays Rhinopteridae and Mobulidae, which together with part of the pectoral fins, forms a pair of cephalic fins; (10) different developmental mechanisms may be responsible for the absence or loss of rostral cartilages in different groups, i.e. absence of the cartilage derived from the medial area of the trabecula in Torpedo vs absence of the rostral cartilage in benthic stingrays; (11) the rostral cartilages in some placental mammals (cetaceans and sirenians) arise only from the medial area of the trabecula because monotreme and placental mammals do not form the trabecula cranii; (12) some actinopterygians and sacropterygians possess a rostral cartilage which originates only from the medial area of the trabecula. One scombroid group, including Sardini and Thunnini, Scomberomorus, Acanthocybium, Istiophoridae and Xiphias, possesses a unique larval beak composed of the rostral cartilage, ethmoid cartilage and premaxillar bone. The development and homology of other rostral cartilages remain to be further elucidated; (13) urodeles possess a medial rostral process whose anlage is probably developmentally equivalent to that in batoid fishes but the occurrence in urodeles is either atavistic or unique (autapomorphic); (14) the upper jaw of tadpoles is unique in possessing the suprarostral cartilage; the anlage of the cartilage is probably developmentally equivalent to the outgrowth of the cornu trabecula in batoid fishes.

It is essential to consider chondrichthyans (cartilaginous fishes) in analyzing ancestral brain organization because this radiation represents the out-group to all other living gnathostomes (jawed vertebrates). It is particularly crucial to understand the evolution of the telencephalon in chondrichthyans, as this structure develops by evagination (as in most other vertebrates), whereas in most osteichthyans (bony fishes), it develops by eversion, a markedly different process. Among chondrichthyans, the Lesser Spotted Dogfish Scyliorhinus canicula (Elasmobranchii) appears to offer the most potential as a model species for study. Developmental studies of Scyliorhinus have revealed a segmentary pattern in the developing forebrain, similar to that described in other vertebrates, as well as the occurrence of tangential cell migration within the telencephalon, especially in relation to the pallial-subpallial boundary. These observations indicate that major morphogenetic processes thought to be a hallmark of mammalian brains actually existed much earlier in vertebrate phylogeny. In addition, analysis of telencephalic development in Scyliorhinus indicates the existence of telencephalic structures that are probably related to the ganglionic eminences of mammals.

Light and electron microscopy of the excretory kidney of adolescent dogfish, Scyliorhinus caniculus (L.), revealed immature and mature nephrons as well as four developmental stages of nephrons. At stage I the nephron was characterized by a condensed mass of mesenchymal cells in the center of several concentric layers of connective tissue. At stage II of the nephron, the S-shaped body was an elongate cyst with a high prismatic epithelium that was connected by a developing collecting tubule with the collecting duct system. At stage III, the developing nephrons already possess the essential features of the mature nephron but lack complete differentiation. Developing renal corpuscles had one afferent arteriole and two efferent vessels. Developing tubules ran four times between the lateral bundle zone and the mesial tissue zone before they joined the collecting duct system. A continuous sheath of flat cells, encompassing the collecting duct system, extended around the developing lateral bundle. A rudimentary central vessel ran from the developing lateral bundle to the venous sinusoid capillaries between the mesial convolutions. Developmental stage IV was similar to the mature nephron, however, renal corpuscles and tubular segments were smaller than those of mature nephrons. Conclusive evidence for morphological homology of elasmobranch nephron segments and collecting tubule-collecting duct system with those of other vertebrates is provided. The origin and nature of the central vessel and the bundle sheath is clarified. These specific structures of marine elasmobranch kidney supposedly are of great functional relevance for the renal countercurrent system that in turn is essential for ion- and osmoregulation.

The taste buds (TBs) of animals of different systematic groups differ considerably in structure [1], but our knowledge of these sensory organs across the vertebrate lineage is currently too limited to derive a TB phylogenetic tree. Since only a single report exists on gustatory receptors of selachians [2], the present study of the structure of TBs of the spotted dogfish, Scyliorhinus caniculus, was initiated to learn more of the interrelationships among TBs of vertebrates. Spotted dogfish were immersion-fixed in a glutaraldehyde-paraformaldehyde-picric acid solution. Pieces of skin removed from different parts of the head and oral cavity were processed conventionally for transmission electron microscopy. In the spotted dogfish, TBs were rare and occurred exclusively at the tip of epidermal papillae within the oral mucosa. In longitudinal section, the TBs were pear-shaped, were approximately 50 μm high and 30 μm wide, were located in the upper third of the squamous non-keratinized epithelium, and were surrounded by marginal cells, the normal epidermal cells. The base of each TB rested on the marginal cells and not on the underlying dermal (corium) papilla, which projected into the basal portion of the epithelium. Each TB was innervated by a nerve that ran through the corium papilla, penetrated the basal lamina of the epithelium, and ascended between the epithelial cells to the TB. Blood capillaries were present in the dermal papilla, but did not reach the TB. The sensory epithelium within the TB consisted of a total of about 25 slender light and dark cells bearing microvilli and situated parallel to the TB’s longitudinal axis. Light cells, which stained less electron dense than dark cells, had a cytoplasm rich in mitochondria, smooth endoplasmic reticulum (sER), and microtubules, and their apical ends terminated in three to five large and divided microvilli. Intermediate (tono)-filaments were rarely observed. Dark cells occurred in two forms. In form one, the cell ended apically in long, slender, and divided microvilli. This dark cell was rich in mitochondria, sER, and dark-staining secretory vesicles of about 200 nm diameter, and contained numerous intermedate filaments. Form two of the dark cell showed long, thin, and undivided microvilli. These form two dark cells contained numerous mitochondria, numerous profiles of the sER, and solitary intermediate filaments. Also, small filament bundles occurred in the basal portions of the cell. Some of the basal marginal cells, which were also rich in organelles, appeared to be basal stem cells, and were different from those of teleosts [1,3,4]. In the spotted dogfish, basal cells comparable to the ones in teleosts did not form the base of the TB, but lay directly on top of the corium papilla. The TB was innervated by unmyelinated nerve fibers, and presynaptic 130-nm dense core and 40-nm clear vesicles occurred mainly at the bases of both the light and dark (form 1) cells. Efferent synapses were not observed. Thus, the TBs of the spotted dogfish differed in the following ways from those of other vertebrates: (1) the TBs were not located directly on top of the corium papillae; (2) the TBs contained at least three types of elongated cells which reached the epithelial surface; and (3) the TBs did not contain basal cells analogous to those of teleosts and amphibians [1,3,4].

The distribution of vasotocin-like peptides in the central nervous system of the cartilaginous fish Scyliorhinus canicula was determined by indirect immunofluorescence and peroxidase anti-peroxidase techniques, using a specific antiserum raised in rabbits against synthetic vasotocin. Immunoreactive perikarya were mainly detected in the anterior hypothalamus, within the midcaudal part of the preoptic nucleus. The most rostral positive cell bodies were located in the dorso-lateral parts of the preoptic area, whereas at a more caudal level, they took a ventro-medial position within the deepest layers of the nucleus. Throughout the preoptic region these cells varied in shape according to their location. Occasionally, scattered vasotocin-like immunopositive cells were also identified in the nucleus periventricularis hypothalami. Vasotocin immunoreactivity was detected in numerous varicose nerve fibers of the preopticohypophysial tract. These fibers were seen to course through the medio-basal hypothalamus and caudally, after having passed the hypophysial stem, they reached the neurointermediate lobe of the pituitary. Numerous immunoreactive fibers were also observed within the rostro-medial region of the median eminence. At this level the fibers were in close proximity to the capillary loops. In the preoptic region, some stained cells exibited short processes that appeared to contact non-reactive perikarya. By comparing the distribution of vasotocin- and corticotropin-releasing factor immunoreactivity on adjacent then serial sections, it was revealed that these peptides, in S. canicula, do not coexist in the same perikarya. The present results, are compared with those obtained in other vertebrate groups, and their possible functional implications are discussed.

As representatives of the vertebrate class of chondrichthyes the plagostomian species Squalus acanthias, Scyliorhinus canicula and Raja clavata as well as the holocephalan species Chimaera monstrosa were investigated for the presence of cardiac hormones of the atrial natriuretic polypeptide/cardiodilatin- (ANP/CDD-) family. ANP/CDD-immunoreactive cells were detected in the atria and the ventricles of all species studied. While these cells failed to react with antisera raised against the N-terminus of CDD-126 (= gamma-ANP) they reacted with all antisera directed against sequences of the C-terminus of CDD-126 (CDD 99-126) which is identical to alpha-ANP. The ANP/CDD-immunoreactive cells were found in high numbers in all regions of the atria and in moderate density also in the ventricles. In correspondence, in the electron microscope, myoendocrine cells which were characterized by dense-cored secretory granules were identified in the atrial and ventricular myocardium. With the use of the protein A-gold technique, ANP/CDD-immunoreactivity was determined within the secretory granules. Furthermore, in the bioassay, prepurified extracts of the atria and the ventricles of Scyliorhinus and Chimaera exerted dose-dependent relaxations of the pre-contracted mammalian (rabbit) aorta. In both cases the atrial extracts proved to be more potent than the ventricular extracts. The present findings indicate that myoendocrine cells occur in the atria and ventricles of chondrichthyes and that these cells contain homologous cardiac hormones of the ANP/CDD-family in their secretory granules. The results are compared with those obtained earlier for the other vertebrate classes and their phylogenetic and functional significance is discussed.

In the dogfish Scyliorhinus degenerating axons and terminals arising from Purkinje cells and resulting from small superficial lesions made in the cerebellar corpus were found to be predominantly restricted to the ipsilateral cerebellar nucleus; none was observed in the tegmentum. Horseradish peroxidase placed within the cerebellar nucleus was transported retrogradely to the Purkinje cells. It appears that in these fishes, as in mammals, cerebellar output is relayed through cerebellar nuclei.

A model for the organization of fibrils in the collagenous egg case of the dogfish Scyliorhinus caniculus is proposed on the basis of observations on ultrathin sections tilted in a goniometer stage. The centrosymmetric transverse banding pattern consists of an A band flanked immediately by two dense C bands which are in turn flanked by broad B bands. In the model, the B bands contain molecular segments packed in a square lattice forming a rectangular prismatic cell parallel to the fibril long axis. The molecules kink in the C band or gradually bend at the ends of the B band to tilt up or down at 25 ° to the fibril axis in the C and A bands. The tilt is such that the corner of one B band unit is body centred on the face of the next B band unit. Our model has similarities to models for the arrangement of type IV collagen in basement membrane, α-actinin in the Z-discs of striated muscle and the intercellular material in spot desmosomes.

The excretory portion of the opisthonephric kidney of Scyliorhinus caniculus displays a mesial zone that is supplied with venous blood by the renal portal system and with arterial blood from the efferent arterioles of the glomeruli, and a zone of lateral bundles that is irrigated with arterial blood via arterioles in parallel to the afferent arterioles of the glomeruli. Each single nephron performs two large convolutions in the mesial tissue and two hairpin loops in the bundle. The nephron is differentiated into renal corpuscle (located between the two zones), neck segment (in the bundle), proximal segment I (beginning in the bundle, major convolution between the zones), proximal segment II (exclusively in the mesial zone), intermediate segment (beginning in the mesial tissue and ending in the bundle), distal segment (exclusively in the bundle) and collecting tubule (beginning in the bundle, with a large convolution in the mesial tissue and ending in the bundle) that joins the collecting duct-ureter system. In the bundles proximal and distal nephron segments, the end of the renal tubule and a central bundle vessel are arranged together and form a complex countercurrent system that is enclosed in a sheath of connective tissue. The bundles provide the structural basis for the creation of an environment with low urea concentration around the final portion of the renal tubules, which is consistent with previous experimental evidence of a significantly lower urea content of the bundles as compared with the blood and the mesial tissue in another marine elasmobranch, Raja erinacea. This condition is thought to lead to passive reabsorption of urea from the fluid of the end of the renal tubule. Separation of individual nephrons in the bundle zone appears to be correlated with the peculiar secondary structure that results from the folding of the bundles and may be in addition a requirement in conjunction with intermittent function of the glomeruli. The zonation of the renal tissue with formation of bundles with counter-current systems is characteristically found in marine Elasmobranchs and is considered to be the morphological correlate to the physiological ability of the marine Elasmobranchii to use urea for osmoregulation.

A description is provided of the mesencephalic nucleus of the fifth nerve (mes. V) and its axonal projections in the brains of dogfish (Scylio-rhinus,Mustelus) and rays (Raja), based upon light microscopic observations. The mes. V nucleus contains 800-1100 cells distributed about the midline at the ventral surface of the optic tectum. Each cell gives rise to a stout axon which courses laterally, then posteriorly on the ipsilateral side; the collected axons divide at the caudal extreme of the tectum into a medial bundle which enters the ventral granular eminence of the anterior cerebellar lobe, and a lateral bundle which enters the medulla and leaves the brain via the fifth nerve root. The medial bundle arises from a cluster of mes. V neurons at the posterior limit of the nucleus which comprise about 15% of the nuclear population. The cerebellar projection ascends the anterior lobe and appears to end in close proximity to Purkinje cell perikarya. A typical mes. V perikaryon is oval, flattened dorsoventrally with average dimensions of 41 µm x 56 µm. It emits a few stout dendrites from its dorsal surface which extend no more than 75 µm from the cell body. Processes from deep tectal cells and collaterals from commissural fibres appear to make synapses upon mes. V perikarya. In addition, neighbouring mes. V neurons often form clusters and also contact each other via short dendrites. A small subpopulation of mes V. neurons gives rise to stout, ventrally directed processes which enter the ependymal layer and ramify within it. These may have a neurosecretory function.

Afferent single fiber impulses were recorded from isolated ampullae of Lorenzini of dogfishes (Scyliorhinus canicula). The ampullae were placed between two thermodes, each of which could be circulated separately with water at 12°, 18° and 24° C, thus allowing cooling and warming with various combinations of spatial temperature gradients. At constant temperature, there was a static discharge in the ampullary fibers. Cooling elicited a dynamic overshoot in frequency, followed by adaptation to a new steady state, whereas warming led to a transient inhibition. Within the limits of error the direction and slope of the spatial temperature gradient had no influence whatsoever on the static and dynamic responses of the ampullae, the only effective parameters being the temperature at the site of the receptor and the rate of temperature change with time.

The vascular bed of the locomotor muscle in three shark species and in a holocephalan is investigated and the capillarization quantified by morphometrical methods. The red muscle fibres of Scyliorhinus, Galeus, Etmopterus and Chimaera are well vascularized having respectively 25, 18, 23 and 5 per cent of fibre surface covered by capillaries. The white muscle fibres of Scyliorhinus are far better vascularized than white muscle fibres of Galeus, Etmopterus and Chimaera. The fibre surface covered by capillaries are 9, 1.4, 0.2 and 1.3 per cent, respectively. The intermediate muscle fibres have a vascular supply between that of red and white muscle fibres in all species. If the capillary contact area to the fibres are related to the mitochondrial volume, more similar values are obtained for the vascular supply to all fibres types in all animals. This parameter indicates that there is a definite relation between the capacity of the oxygen transport system and the aerobic metabolic machinery.

An elevation of the pectoral fin generated reflexly by electrical stimulation of the fin was studied in decerebrate dogfish (Scyliorhinus) by recording the electromyogram from the levator muscle. This pectoral fin reflex had two components: a phasic lift of the fin lasting for 70–100 ms, followed by a sustained (tonic) elevation lasting for 500–1,000 ms or more. Ablation of the cerebellum resulted in a pronounced depression of the reflex which particularly affected the tonic component. Division of the brainstem at the level of the obex restored both components to the reflex and frequently led to spread of activity to other muscles. It is suggested that in this animal the brainstem generates a powerful tonic inhibitory drive directed at spinal motor circuits and that the cerebellum modulates precisely this inhibitory influence to permit effective and efficient movement.

The extrinsic nerves of the stomach of dogfish and skates regulate the frequency and amplitude of contraction by inhibition followed by rebounds. By contrast the nerves of the spiral intestine are excitatory.Stimulation of the vagus nerve of the ray produced slight reduction in the amplitude of spontaneous contractions of the cardiac stomach. Much greater inhibition was produced by stimulation of the sympathetic nerves and was followed by large rebound contractions. These effects were imitated by adrenalin and serotonin which altered the frequency and amplitude of contraction in various ways. These actions were not blocked by either propranalol (1–5 × 10−5 M) or phentolamine (2 × 10−5 M) and indeed were often increased. The excitatory response to adrenalin was not blocked by TTX even after this had blocked the response to the nerve. Responses both to the nerve and adrenaline were blocked by trazodone. Acetyl choline caused some contraction of the stomach but only at high concentration.Muscles of the spiral intestine of Raja or Scyliorhinus were activated by stimulation of their sympathetic nerves and by adrenalin. These responses were not blocked by phentolamine and only reduced by propranalol They were blocked by trazodone. The response to adrenalin continued after the nerve was blocked by TTX. Acetyl choline had very little effect on the spiral intestine.The striking differences between the responses of the stomach and intestine are probably related to the fact that the plexus in the latter contains no nerve cells. The neurons in the stomach are therefore presumbly connected with the inhibition and large rebound contractions.

Efferent neurons of the lateral-line organs of dogfish (Scyliorhinus) have been identified in the anterior lateral-line lobe of the medulla. They were identified histologically by filling them with cobalt salts passed electrophoretically along the lateral-line nerve fibres from their cut peripheral ends; in this way multipolar neurons in the rostral region of the lobe were filled with salt (Fig. 1B).

Retinofugal pathways in the spotted dogfish Scyliorhinus canicula and the thornback ray Raja clavata were studied with reduced silver techniques following unilateral eye enucleations. Optic nerve axons decussate in the chiasma opticum, except for a small ipsilateral projection to the area preoptica. After crossing, retinal projections distribute to the area preoptica, the thalamus dorsalis pars lateralis, the thalamus ventralis pars lateralis, the corpus geniculatum laterale, the nucleus pretectalis, and the superficial layers of the tectum mesencephali. In Scyliorhinus most primary optic fibers terminate in the stratum medullare externum of the mesencephalic tectum, while in Raja the zona externa of the stratum cellulare externum receives the bulk of the retinal input. A basal optic tract could be identified in Raja, but not in Scyliorhinus. The retinofugal pathways of the two species studied are compared with those of other cartilaginous fishes and other anamniotes. It is concluded that the primary visual system in chondrichthyans resembles that of actinopterygians and amphibians. However, there is a striking difference in the way in which the primary optic fibers reach the tectal target areas. In elasmobranch fish the optic nerve fibers enter the tectum through the zona interna of the stratum cellulare externum and send their axons into the more superficial tectal layers, while in actinopterygians and amphibians the majority of the optic fibers enter the tectum through the superficial layer and distribute their axons to deeper tectal layers.

The reflecting layer or chorioidal tapetum in the eye of many selachians was examined to determine, especially, whether it is a set feature or whether it can be occluded.Many selachians have a tapetum under the entire fundus of the eye. It consists of highly reflecting cells, towards the outer ends of which there is a layer of melanophores. In active pelagic sharks of the neritic zone (e.g. Squalus, Mustelus), the melanophores send out pigment over the reflecting cells so as to conceal them when the fish is illuminated; the pigment retreats in darkness. In benthic species of the neritic zone, notably Scyliorhinus, the fundus has a black ventral area; a tapetum occurs elsewhere and is not occlusible. The eyes of rays have a black ventral field, and pigment migration over the tapetum is slight. The tapetum is not occlusible in deep-sea squaloids and a chimaerid Hydrolagus affinis.Reflectivity of the dark-adapted tapetum of Squalus acanthias amounts to about 85%. Full expansion of pigment in the light and retreat in darkness occupy about 2 hr in this fish.Pieces of tapeta, freed of retinae, were mounted in Ringer solution, observed, and photographed by oblique illumination from above. The tapetal pigment migrates inwards over the reflecting plates in such preparations of tapeta from fishes that have occlusible tapeta.The suggestion is offered that the tapetum is concealed, either by closure of the pupil or by migration of pigment, so as to avoid displaying eye-shine. Deep-sea squaloids, living in dimly lit environments, do neither.

Hypophysial vascularization is described in members of the genera Squalus, Etmopterus, Scyliorhinus, Pristiurus and Raja. The anterior lobe lacks arteries and is supplied by a pituitary portal system. The collecting area of this system covers the median eminence, but also receives capiIIaries from adjacent hypothalamic nuclei. The two regions of the anterior lobe belong to different regions of the portal system. The neuro-intermediate lobe is usually supplied with arteries, but in some cases receives vessels from the median eminence (Scyliorhinus, Raja). There is a possibility of neurovascular control of the intermedia through vessels from the neural lobe (Squalus, Etmopterus). Lateral afferent veins bring blood from a wide hypothalamic area to or through the neuro-intermediate lobe (not in Squalus). The functional significance of the vascular pathways is, discussed, and an attempt at an evolutionary derivation of the portal system is given.

Summary 1 This paper describes the subcutaneous venous system of Scyliorhinus (Scyllium) caniculus, the Common Dogfish. Previously no complete account of this system appears to have been given for any Selachian. 2 Practically the whole surface of the animal is covered by a dense network of veins. 3 In the trunk and tail these superficial networks drain into dorsal, ventral, and lateral longitudinal vessels. 4 In the pharyngeal region the superficial networks are connected directly to the underlying venous sinuses. 5 The veins of the fins are connected to the cutaneous venous system. 6 Immediately below the skin lining the mouth and pharynx are the bucco-pharyngeal networks of veins. They cover both the dorsal and ventral walls of these cavities, and drain into the principal sinuses of the anterior part of the fish. Posteriorly they are continuous with a fine plexus of vessels surrounding the esophagus. Only the dorsal bucco-pharyngeal vessels have been previously described.

The respiratory movements of the dogfish, ScyUorhinus (Scyllium) canicula (L.), and the ’skate’, Raia clavata L. (thornback ray), have been studied by the use of cinematographic and mechanotransducer recording methods. Simultaneous determinations of the time-course of pressure changes in the oro-branchial and parabranchial cavities were also made by means of Hansen condenser manometers. In both species movements of the mouth precede those of the spiracular valve and of the branchial region. Adduction and abduction of the branchial region spreads serially from the first to last gill slit in the dogfish, but movements of the individual gill arches are more nearly synchronous in the skate. Opening of the flap valves formed by extensions of the inter-branchial septa are synchronous in both species. Water entering one side of the mouth leaves by the three posterior gill slits of the same side. Water entering the spiracle leaves through the anterior slits of the same side. This separation of flow is less marked in the skate. The pressure curves recorded in all parts of the system have both positive and negative phases with respect to the external medium. The positive phase, associated with closing of the mouth and spiracle, is larger in the oro-branchial than in the parabranchial cavities and vice versa. The time-course of the pressure changes indicates that the flow across the gills is maintained by the action of a pressure pump in front and a suction pump behind. The suction pump plays a more important role than the pressure pump in the skate and its contribution to the flow across the gills is by no means negligible in the dogfish. The differential pressure curves suggest that the flow across the gills is continuous except in the dogfish for a brief period when the gradient is reversed. The absence of this reversal in the skate suggests that the external gill slit openings are controlled by an active mechanism. This is probably an adaptation to bottom-living habit. All these observations relate to animals which are stationary with respect to the water. During swimming at a reasonable speed leopard sharks (Triakis semifasciata) have been observed to make few or no respiratory movements, although they immediately ventilate actively on coming to rest at the bottom of the aquarium.

The locomotory musculature of dogfish is innervated by the segmental spinal nerves. The sensory and motor innervation of the abdominal musculature was studied in a preparation consisting of a strip of the abdominal body wall innervated by the ventral rami of the spinal nerves.Each ventral ramus consists of two separate nerve bundles which were found to be peripheral extensions of the dorsal and ventral spinal roots. Recordings from the sensory bundles showed that there are few sensory endings in the musculature and body wall of the dogfish. It was possible to differentiate between ephemeral responses produced by cutaneous free-nerve endings and prolonged discharges which were generated by more specialized sensory endings. In some details these endings were found to be unlike either muscle spindles or tendon organs. Further, skinning experiments suggested that these mechanoreceptors lay in the skin or the very outer layers of the myotome.Histological searching, together with physiological isolation of units, suggested that these receptors were the corpuscular endings distributed sparsely amongst subcutaneous tissue. These endings are apparently the same as those described by Wunderer (1908) in the fins of elasmobranchs.

The sense organs of the body lateral-line canals ofScyliorhinuswere examined with the electron microscope and shown to consist of supporting cells and two kinds of sensory cell. One type of sensory cell has the well-known structure of hair cells, bearing on its apical surface a group of stereocilia (6 to 25) associated with a single kinocilium. Each hair cell is innervated by a sensory nerve fibre and some also receive an efferent nerve supply. The second kind of sensory cell is similar in appearance, but differs at the apex in containing many vacuoles and in lacking stereocilia. There are many long microvilli and a single cilium which arises from a shallow pit. The internal structure of this cilium is variable, with the number of tubules in the outer ring ranging between 7 and 9 and with the inner pair consisting of double elements. This type of sensory cell is innervated by sensory nerve fibres and possibly by efferent fibres. The situation of the kinocilium of a hair cell in relation to the stereocilia is more variable than has been described in other hair cells while the cilium of the second sensory cell appears to bear no special relation to the microvilli. The accessory cells of the neuromast include basal and peripheral supporting cells, many of which produce a secretion, and a large secretory cell which is found at intervals at the edge of the organ. This cell has a convoluted surface and is full of vesicles.

The problems of the nature of the contractile mechanism, nervous control of the iridial muscles, and the control of the batoid operculum pupillare were investigated. Electronmicroscopy revealed the presence of myofilaments in the sphincter (diameter 40–100 A) and dilator (diameter 40–90 A) of Mustelus mustelus, Scyliorhinus canicula, Dasyatis violacea, and Myliobatis aquila, and established the muscular nature of this tissue of epidermal origin. Neuromuscular junctions were found in the dilator of all four species, but in the sphincter of only Mustelus and Scyliorhinus, the latter finding quite unexpected. Both a dilator and sphincter-like muscle were found in the operculum of the batoids, complete with nerve endings, establishing the muscular nature of this important pupillary occluding organ. Nerve endings contained predominantly agranular (diameter 450–800 A) and a few larger granular (diameter 700–1300 A) vesicles. Those in the dilator are known to be cholinergic, those in the sphincter and operculum are unidentified pharmacologically.

A brief description is given of some features in the special morphological organization of the neuromuscular system in the embryo of the lower vertebrates. The development of locomotory behaviour patterns in elasmobranchs is compared with that in other groups. The earliest movements of the embryo of Scyliorhimis caniculus have been photographically recorded ; the results of Wintrebert are confirmed. The movements persist unchanged after complete removal of the nervous system ; they are rhythmical and independent on the two sides. Any isolated portion of an actively contracting myotome band can act as its own pace-maker. The histological structure of the nerve cord and muscle at the time of these first movements is described in detail. There is strong evidence against any morphological link between the motor neurons and the myotome band; other neurons in the developing spinal reflex arc are similarly unconnected with one another. The results are discussed in relation to similar phenomena in other systems. Consideration is given to the mechanism of the excitation and transmission of the contractile process in the myotome band.

An account is given of an hermaphrodite specimen of Scyliorhinus caniculus with asymmetrical ducts and claspers. Possible causes of abnormalities in the reproductive system are discussed.

SUMMARY. A brief description is given of a predominantly male dogfish in which the Mullerian ducts have persisted.

Some neurons of the anterior lateral-line lobe of dogfish (Scyliorhinus) have synapse-bearing perikarya enclosed by layers of compact myelin. The identity of these cells, which have myelinated axons and unmyelinated, synapse-bearing dendrites, is unknown.

Serial sections ranging from very young embryos to hatched juveniles and whole embryos of Scyliorhinus show that dentition and dermal skeleton belong to two independent secondary developmental fields that differ both developmentally and structurally. The development of the dentition starts very early, with a thickening of the ectoderm in the region of the mouth (stage 04), the invagination of the dental lamina (stage 18), and the formation of the germs of the first generation (stage 20). Tooth replacement movements start only near the end of embryogenesis (stage 35). Scale germs, on the other hand, first begin to form at stage 24. Scales erupt shortly before the animal hatches (stage 43). Only one scale generation is formed during embryogenesis. The forces which erupt the scales may come from fluid pressures in vacuoles of the fibrous layer of the dermis. Those which erupt the teeth probably also result from similar fluid pressures. The crown and upper part of the base of scales and teeth are formed by cells of the inner dental epithelium which are differentiated from the ectoderm. They are also formed by odontoblasts which are derived from the vascular layer of the dermis. However, the basal plates of scales and teeth containing the anchoring fibers are formed by osteoblasts, which are derived from the fibrous layer of the dermis.

The cells of origin of pathways descending to the spinal cord in the shark Scyliorhinus canicula and in the ray Raja clavata have been demonstrated by using the horseradish peroxidase (HRP) technique. Following HRP injections in the spinal cord of Scyliorhinus (fourth to sixth segment) and of Raja (15th to 20th segment) labeled neurons could be identified in the rhombencephalon, the mesencephalon, and in the diencephalon. Cells of origin of diencephalic nuclei, which project to the spinal cord, were observed in the nucleus periventricularis hypothalami and in the thalamus ventralis pars medialis which can in this respect be considered hypothalamic. Descending pathways from mesencephalic structures originate from the interstitial nucleus of the fasciculus longitudinalis medialis, the tectum mesencephali, the nucleus intercollicularis, the tectotegmental junction zone, and from diffusely arranged tegmental neurons. A contralateral rubrospinal pathway could be recognized in Raja, but not in Scyliorhinus. Rhombencephalic cells of origin of pathways descending to the spinal cord were found in all parts of the reticular formation, i.e., the nucleus raphes inferior, the nucleus reticularis inferior, medius, superior, and isthmi, in two vestibular nuclei, and in three nuclei, which have been tentatively indicated as nucleus B, F, and G. Furthermore cells of origin of descending pathways have been found in the nucleus tractus descendens nervi trigemini, in the nucleus funiculi lateralis, and in the nucleus tractus solitarii. The descending pathways of the two species studied have been compared with those of other vertebrates. It is concluded that the basic pattern in the organization of descending pathways to the spinal cord, as proposed by ten Donkelaar ('76) for terrestrial vertebrates, also holds for cartilaginous fishes.

1. A comparative quantitative study on the occurrence of 5-HT in several tissues and organs of the elasmobranch Scyliorhinus stellaris and the teleost Conger conger has been carried out. 2. In Scyliorhinus, the richest source of the amine is the brain, in which 5-HT is twice as concentrated as in the teleost brain. Significant levels have been also detected in the intestine, followed by gills and heart. 5-HT is also concentrated in other epithelial organs, such as the rectal gland and the olfactory organ. 3. In Conger, the gills show the highest content of 5-HT, in which, like in the kidney, serotonin is 2-3 times more concentrated than in the corresponding organs of the elasmobranch. 4. These differences are discussed in relation to the distinct phylogenetic and ecophysiological features of the two animals. In addition, the possible functional significance of 5-HT in the fish heart is taken into consideration. © 1983.

The afferent connections of the tectum mesencephali were studied in the spotted dogfish Scyliorhinus canicula and the thornback ray Raja clavata by means of the horseradish peroxidase (HRP) technique. Following unilateral injections in the tectum, labeled neurons could be identified in all main divisions of the brain and in the cervical spinal cord. Telencephalic neurons which project to the tectum mesencephali were observed in the caudal part of the pallium. Diencephalic projections to the tectum originate from the thalamus dorsalis pars medialis, the thalamus ventralis pars lateralis, the nucleus medius infundibuli, and the pretectal area. In Scyliorhinus labeled neurons could also be found in the corpus geniculatum laterale. Mesencephalic cells of origin of tectal afferent pathways were identified in the stratum cellulare externum of the contralateral tectum, in the nucleus tegmentalis lateralis, in the ventrolateral tegmentum, and in the nucleus ruber. Rhombencephalic cells projecting to the tectum could be identified in the nucleus cerebelli (only in Scyliorhinus), the nucleus vestibularis superior, the reticular formation, the nucleus funiculi lateralis, the nucleus tractus descendens nervi trigemini, and the nucleus dorsalis and intermedius areae octavolateralis. In addition a number of small-and medium-sized cells of the reticular formation were found labeled. Diffusely scattered labeled cells could be observed in the dorsal part of the cervical spinal cord. It is concluded that the tectal afferent connections in the chondrichthyans studied in general resemble those of other vertebrates, but that some striking differences exist. In particular, tectal afferents originating from the nucleus medius infundibuli, the nucleus cerebelli, and the nucleus dorsalis and intermedius areae octavolateralis have not been reported in other vertebrates.

Patterns of activity of cerebellar neurones in response to cutaneous stimulation and during spontaneous, swimming-like movements were examined, using microelectrodes, in decerebrate dogfish (Scyliorhinus canicula). Continuous swimming movements, lasting for several hours, were obtained in fish in which the medial longitudinal fasciculus (m.l.f.) was lesioned in the rhombencephalon. Purkinje cells (P cells) and some stellate cells (S cells) were observed to discharge rhythmically, in phase with swimming movements. These units were distributed throughout the cerebellum, but with no apparent somatotopic distribution. After curarization, rhythmic motor discharges could still be recorded from ventral roots and phase locked P cell discharges were recorded from the cerebellum. P cells that discharged rhythmically during active swimming movements, did not do so when the body was oscillated passively during quiescent periods. Cutaneous stimulation evoked burst discharges in many P cells at long latency (ca. 100 ms) both before and after curarization and whether or not a rhythmic motor output was being generated. In rhythmically discharging units, a similar response was obtained when cutaneous stimulation was applied during that part of a cycle when the unit was most or least active. It was concluded that cerebellar neurones discharged in phase with the output of the spinal locomotory rhythm generators and independently of peripheral sensory feed-back.

The ventricular sulcal pattern and the cellular structure of the brain stem of the sharks Squalus acanthias and Scyliorhinus canicula have been studied in transversely cut Nissl, Kluver-Barrera and Bodian stained serial sections. Five longitudinal sulci, the sulcus medianus inferior, the sulcus intermedius ventralis, the sulcus limitans, the sulcus intermedius dorsalis and the sulcus medianus superior could be distinguished in both species. In addition to these long, principal grooves, a number of shorter, accessory sulci appeared to be present. Although the neuronal perikarya in many places display a diffuse arrangement, with the aid of the usual cytoarchitectonic criteria 34 cell masses could be delineated in Squalus and 30 in Scyliorhinus. These cell masses can be distributed over the following categories )numbers added in brackets for Scyliorhinus, if different from those in Squalus(: primary efferent or motor, 10 )9(; primary afferent or sensory, 7: reticular formation, 5; “relay” centers, 9 )8(; nuclei of unknown relationships, 3 )1(. Seven of the cell masses found in Squalus and four of those found in Scyliorhinus have not been described before. The morphological pattern of the cell masses and their relationship to the ventricular sulci were studied with the aid of a graphical reconstruction procedure termed topological analysis )cf. Nieuwenhuys, '74, and figs. 24, 25(. This analysis yielded for both sharks the following results: A sulcus limitans extends from the spinal level to the pretrigeminal region. This sulcus divides the greater part of the rhombencephalon into a basal plate and an alar plate. In the basal plate the sulcus intermedius ventralis marks the boundary between an area ventralis and an area intermedioventralis. The area ventralis contains two somatic motor centers )i.e., the rostral end of the spinal motor column and the medial part of the nucleus of VI( and by far the greater portion of the rhombencephalic medial reticular formation. The latter may be primarily considered as a somatic motor coordinating center. The area intermedioventralis contains the visceral motor nuclei of X, IX, VII and V. However, the basal plate also harbours a number of non-motor centers, for example the inferior olive and the nucleus funiculi lateralis. In the caudal half of the rhombencephalon the sulcus intermedius dorsalis subdivides the alar plate into an area intermediodorsalis and an area dorsalis. The area intermediodorsalis is largely occupied by the common visceral sensory center of X, IX and VII; however, this area also contains the general somatic sensory nucleus descendens of V and the nucleus vestibularis magnocellularis. The area dorsalis is entirely occupied by two large lateral line nerve centers. The cell masses in the isthmus region and in the mesencephalon do not exhibit a clear-cut morphological pattern. Functionally, however, a number of centers in the medial part of the tegmentum mesencephali )nuclei of IV and III, nucleus of the f.l.m., nucleus ruber( may be considered as a rostral continuation of the rhombencephalic somatic motor area. Similarly, the nucleus of Edinger-Westphal represents the visceral motor zone at the midbrain level. The lateral part of the tegmentum mesencephali contains the nucleus of the torus semicircularis and the nucleus tegmentalis lateralis. It is suggested that these two nuclei together constitute a zone of somatic sensory relay centers.

In a single-fibre preparations the afferent discharges from prepolarized ampullae of Lorenzini responding to graded temperature steps were investigated in the dogfish (Scyliorhinus canicula). The transformation characteristics of the ampullary receptors, especially their differential thermosensitivity interfering with electrosensitivity, were analyzed. Prepolarization significantly influenced the dynamic component of differential thermosensitivity, while the static component remained practically unchanged. Hyperpolarization reduced positive and negative dynamic thermal responses; depolarization amplified them. Biological consequences of this bimodal interference for receptor transformation of superimposed thermal and electric stimuli and for decoding afferent ampullary impulse patterns are discussed.

IN this report, observations of ultrastruetural organization of neurosecretory elements of the neurointermediate lobe in two types of the Black Sea skates, Raja clavata and Trygon pastinaca, are considered. As was shown in our earlier work with the light microscope1, the axoadenar neurosecretory contacts in these types of skates are well developed and very distinct. In the literature there appears to be only one report2 in which the axoadenar contacts with the adenohypophysis elements in Scyliorhinus caniculus (L) were examined with the electron microscope, and some other work done on teloosts3–5.