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The complete mitochondrial DNA sequence of the Nursehound Scyliorhinus stellaris has been determined for the first time and compared with congeneric species. The mitogenome sequence was 16,684 bp in length. The mitogenome is composed of 13 PCGs, 2 rRNAs, 22 transfer RNA genes and non-coding regions. The gene order of the newly sequenced mitogenome is analogous to the organization described in other vertebrate genomes. The typical conservative blocks in the control region were indicated. The phylogenetic analysis revealed a monophyletic origin of the Scyliorhininae subfamily, and within it, two subclades were identified. A significant divergence of Scyliorhinus spp. together with Poroderna patherinum in relation to the group of Cephaloscyllium spp. was observed, except for Scyliorhinus torazame, more related to this last cited clade. A hypothesis of a divergent evolution consequent to a selective pressure in different geographic areas, which lead to a global latitudinal diversity gradient, has been suggested to explain this phylogenetic reconstruction. However, convergent evolution on mitochondrial genes could also involve different species in some areas of the world.

Intersexual differences in morphometrics were investigated in five species of the catshark genus Scyliorhinus. ANCOVA was used to test 59 measurements, considering capture location and total length as covariates. In all examined species, pelvic-anal distances and pelvic-fin inner margin lengths were greater in males than in females, representing a clear pattern for the genus.

The catshark genus Scyliorhinus belongs to the family Scyliorhinidae, the most diverse family of sharks, and currently presents 16 valid species according to most modern accounts. The long history of taxonomic rearrangements and inaccurate descriptions of many species have contributed to misidentification of specimens and lack of information on the distributional range and diagnostic characters of its species. Species of Scyliorhinus are reviewed and redescribed here, with detailed descriptions on external morphology, neurocranium, claspers, dermal denticles, and tooth morphology provided for the first time for all species. Sixteen species are recognized as valid: Scyliorhinus boa (Goode & Bean, 1896), S. cabofriensis Soares, Gomes & de Carvalho, 2016, S. canicula (Linnaeus, 1758), S. capensis (Müller & Henle, 1838), S. cervigoni Maurin & Bonnet, 1970, S. comoroensis Compagno, 1988, S. duhamelii (Garman, 1913), S. garmani (Fowler, 1934), S. haeckelii (Miranda Ribeiro, 1907), S. hesperius Springer, 1966, S. meadi Springer, 1966, S. retifer (Garman, 1881), S. stellaris (Linnaeus, 1758), S. torazame (Tanaka, 1908), S. torrei Howell-Rivero, 1936, and S. ugoi Soares, Gomes & Gadig, 2015. The main taxonomic decisions herein taken include the resurrection of S. duhamelii (previously a junior synonym of S. canicula) and the synonimization of S. tokubee with S. torazame. Information on geographic distribution was updated for most species, especially for those with wide ranges (S. canicula, S. haeckelii, S. retifer, and S. stellaris).

In amniotes, limb muscle precursors de-epithelialize from the ventral dermomyotome and individually migrate into limb buds. In catsharks, Scyliorhinus, fin muscle precursors are also derived from the ventral dermomyotome, but shortly after de-epithelialization, they reaggregate within the pectoral fin bud and differentiate into fin muscles. Delamination of muscle precursors has been suggested to be controlled by hepatocyte growth factor (HGF) and its tyrosine kinase receptor (MET) in amniotes. Here, we explore the possibility that HGF/MET signaling regulates the delamination of appendicular muscle precursors in embryos of the catshark Scyliorhinus canicula. Our analysis reveals that Hgf is expressed in pectoral fin buds, whereas c-Met expression in fin muscle precursors is rapidly downregulated. We propose that alteration of the duration of c-Met expression in appendicular muscle precursors might underlie the evolution of individually migrating muscle precursors, which leads to the emergence of complex appendicular muscular systems in amniotes.

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.

Sharks of the genus Scyliorhinus from the southwestern Atlantic are reviewed; identification problems and taxonomic misinformation given in the literature are rectified. After extensive examination of the external and internal morphology of specimens collected mostly off southeastern and southern Brazil, Scyliorhinus besnardi Springer & Sadowsky, 1970 is placed in the synonymy of S. haeckelii (Miranda Ribeiro, 1907), which is thoroughly redescribed. Additionally, a new species, Scyliorhinus cabofriensis, sp. nov., is described from the state of Rio de Janeiro, distinguished from all southwestern Atlantic congeners by its color pattern, clasper and neurocranial morphology, and proportional measurements. A key to Scyliorhinus species occurring in the southwestern Atlantic is also provided.

Biofluorescence has recently been found to be widespread in marine fishes, including sharks. Catsharks, such as the Swell Shark (Cephaloscyllium ventriosum) from the eastern Pacific and the Chain Catshark (Scyliorhinus retifer) from the western Atlantic, are known to exhibit bright green fluorescence. We examined the spectral sensitivity and visual characteristics of these reclusive sharks, while also considering the fluorescent properties of their skin. Spectral absorbance of the photoreceptor cells in these sharks revealed the presence of a single visual pigment in each species. Cephaloscyllium ventriosum exhibited a maximum absorbance of 484 ± 3 nm and an absorbance range at half maximum (λ1/2max) of 440–540 nm, whereas for S. retifer maximum absorbance was 488 ± 3 nm with the same absorbance range. Using the photoreceptor properties derived here, a “shark eye” camera was designed and developed that yielded contrast information on areas where fluorescence is anatomically distributed on the shark, as seen from other sharks’ eyes of these two species. Phylogenetic investigations indicate that biofluorescence has evolved at least three times in cartilaginous fishes. The repeated evolution of biofluorescence in elasmobranchs, coupled with a visual adaptation to detect it; and evidence that biofluorescence creates greater luminosity contrast with the surrounding background, highlights the potential importance of biofluorescence in elasmobranch behavior and biology.

Het gaat wereldwijd niet goed met haaien en roggen. Geldt dat ook voor de Noordzee? Welke eigenschappen maken haaien en roggen zo bijzonder en tegelijkertijd kwetsbaar en welke maatregelen kunnen genomen worden om te voorkomen dat er soorten uit de Noordzee verdwijnen?

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.

Het gaat wereldwijd niet goed met haaien en roggen. Geldt dat ook voor de Noordzee? Welke eigenschappen maken haaien en roggen zo bijzonder en tegelijkertijd kwetsbaar en welke maatregelen kunnen genomen worden om te voorkomen dat er soorten uit de Noordzee verdwijnen?

1. 1. Testes of the dogfish, Scyliorhinus caniculus , were incubated with [ 3 H]pregnenolone and [ 3 H]testosterone at a range of temperatures from 1 to 36°C. 2. 2. Yields of testosterone from pregnenolone were maximal between 11 and 16°C, corresponding to the breeding temperature of the species. 3. 3. Yields of glucuronides and sulphates increased from 1 to 26°C. 4. 4. Yields of an unidentified polar metabolite increased with temperature and it is suggested that this may play a regulatory role in elasmobranch reproduction.

A peptide fraction has been purified from intestinal extracts of the dogfish Scyliorhinus canicula which is a powerful stimulant of rectal gland secretory activity. This peptide is distinct from elasmobranch vasoactive intestinal polypeptide (VIP). The elasmobranch VIP fraction is not active in the rectal gland assay and mammalian VIP is only an effective agonist in Squalus and not in Scyliorhinus or Raja. Preliminary characterisation of the elasmobranch VIP indicate that it has strong N-terminal similarities with mammalian VIP but has limited C-terminal comparability. It is suggested that the rectal gland stimulating peptide, rectin, rather than VIP is responsible for the control of fluid and electrolyte secretion of elasmobranchs.

The peptidergic nature of most of the fibres of the neurosecretory system of Scyliorhinus caniculus has been demonstrated with the oxidation method of Naumann and Sterba (1976). Some of the fibres of this peptidergic system terminate on capillaries in the hypothalamic floor, some on neurointermediate cells. The evolutionary aspects of these observations are discussed.

A simple radioimmunoassay method for the simultaneous determination of 1α-hydroxycorticosterone, 1-dehydrocorticosterone, corticosterone, and cortisol in small samples of elasmobranch plasma has been developed. Chromatographic separation of these steroids, followed by acid dehydration of 1α-hydroxycorticosterone and chromatography and subsequent radioimmunoassay of the resultant 1-dehydro derivative using an antibody raised for corticosterone, gave a highly specific and sensitive method for the determination of 1α-hydroxycorticosterone. 1α-Hydroxycorticosterone concentrations in the ray Raja clavata ranged from less than 0.08 to 13.9 μg/100 ml of plasma, and in the dogfish Scyliorhinus caniculus from 0.1 to 0.54 μg/100 ml of plasma. This compound was not detected in the rainbow trout Salmo gairdneri . Corticosterone and 1-dehydrocorticosterone were either undetectable or were present in extremely low concentrations in both species of elasmobranch. Cortisol, the major corticosteroid in the rainbow trout (8 μg/100 ml), was not detectable in either of the elasmobranch species.

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 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.

1. 1. The AMP deaminase from erythrocytes from the dogfish, Scyliorhinus caniculus , L., was purified by chromatography on cellulose-phosphate and DEAE-cellulose. 2. 2. The 1300-fold purified enzyme was highly unstable. 3. 3. At low substrate concentrations, a sharp pH optimum was found at pH 6.7. At higher substrate concentrations, the highest activity was found between pH 6.8 and 7.2. 4. 4. The substrate saturation curve was hyperbolic in the presence of monovalent cations. The binding of inorganic phosphate showed cooperativity. 5. 5. Overall the kinetic properties of AMP deaminase from erythrocytes from dogfish are very similar to that described for other species.

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.

1. Previous experiments have demonstrated that ( a ) the shark Scyliorhinus canicula and the ray Raja clavata are extremely sensitive to weak electric fields; ( b ) their electrical sensitivity is due to the ampullae of Lorenzini; ( c ) the sharks and rays can be stimulated by the bioelectric fields emanating from the flatfish Pleuronectes platessa . 2. When hungry, Scyliorhinus and Raja perform well-aimed feeding responses to flatfish, even if the prey have covered themselves with sand. The object of the present study was to determine whether the sharks and rays use the bioelectric fields of the flatfish to detect the position of their prey. 3. To analyse the feeding responses of the sharks and rays, a flatfish was put into an agar chamber. The predators responded to the so screened prey from the same distance, and tried to feed on it in the same way as if there were no agar at all. As the flatfish in the agar chamber was completely hidden from view, the sharks and rays were thus shown not to need visual contact to locate the prey. 4. If the agar chamber was filled with cut-up pieces of whiting, the sharks and rays did not respond to the food, although the odour of whiting juice normally attracts them strongly. Therefore, the sharks and rays did not detect the position of the agarscreened flatfish by smell. 5. The feeding responses to the flatfish could be entirely abolished by covering the agar chamber with a very thin sheet of plastic. The mechanical attenuation offered by the plastic film was too weak to explain its dramatic inhibitory effect, and, thus, a purely mechanical detection of the agar-screened flatfish without plastic film was also ruled out. 6. As the responses to the agar-screened flatfish were not merely due to visual, chemical, or mechanical stimuli, it was tentatively concluded that the sharks and rays perceived the prey electrically. This conclusion was fully in agreement with the results of the experiments, for the agar chamber did not appreciably distort the bioelectric fields of the flatfish, and the electrical impedance of the plastic film was extremely high. 7. Further, the bioelectric field of a flatfish was simulated with a pair of electrodes, buried in the sand. Now, the sharks and rays displayed exactly the same feeding responses to the electrodes as they did previously to the real prey. This crucial experiment confirmed the electrical hypothesis in a very direct way. 8. The experiments described demonstrate clearly that the shark Scyliorhinus canicula and the ray Raja clavata make a biologically significant use of their electrical sensitivity. Therefore, we now are justified in accrediting the animals with an electric sense and in designating the ampullae of Lorenzini as electroreceptors . 9. When the sharks and rays were offered a piece of whiting in the vicinity of two electrodes simulating a flatfish, they were attracted by the odour of the food but usually performed their well-aimed responses to the electrodes. Thus, at short range, the electric fields act as a much stronger directive force than do the visual and chemical stimuli. Only direct mechanical contact dominates over the electrical stimuli. 10. Theoretically, the sharks and rays can detect the electric fields resulting from ceanic and tidal currents. Whether they make use of the available information for orientation in the open sea is not yet known. Furthermore, the observations and measurements described indicate that, in studying shark attacks, the electric fields of the prey and the electric sense of the predators should be taken into account. Present address: Department of Neurosciences, School of Medicine, University of California, San DiegoLa Jolla, California 92037.

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.

Pituitary extracts from species representing subgroups of the cartilaginous fishes were investigated for the presence of neurohypophyseal principles. Paper chromatography of pituitary extracts from Raia clavata and Scyliorhinus caniculus yielded two major oxytocic fractions. The pharmacological characteristics of the two components were determined by multiple bioassay, which showed differences between them. The presence of a trace of a vasotocin-like principle in Scyliorhinus extracts was also indicated by chromatography. Pituitary extracts of Squatina squatina and Rhinobatis rhinobatis also yielded two fractions. The fast-moving components of both S. squatina and R. rhinobatis extracts had similar Mg2+ potentiation ratios. The slow-moving fraction of Rhinobatis was similar to that of Scyliorhinus. Bioassays of the slow-moving fraction of Squatina indicated the presence of vasotocin. Pituitary extracts of Carcharinus leucas and Negaprion brevirostris were chromatographically resolved into two fractions. The fast-moving principles of these two species showed similar pharmacological properties as those of other selachians; no definite conclusion could be reached as to the nature of these active fractions. Chromatography of Hexanchus griseus pituitaries yielded one major oxytocic region. The active principle was not potentiated by magnesium. Paper chromatograms of holocephalian (Chimaera monstrosa, Hydrolagus collei, and Callorhynchus sp.) pituitary extracts showed two oxytocic regions. Neither of the two fractions was potentiated by magnesius.

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.

Among vertebrates, chondrichthyans exhibit peculiar karyotypes and total amount and composition of DNA very different from those of tetrapods and teleosteans. Selachians have relatively large genome sizes (more than 30 pg/N), which are inversely related to the fraction rich in adenine‐thymine. Moreover, they show a high chromosome number (2n = 60–100), decreasing in the most specialized species. The karyotypes of Scyliorhinus stellaris, Torpedo ocellata, and T. marmorata have been investigated by several techniques in order to distinguish particular genome fractions along the chromosome arms. C‐banding appears to be positive in most telomeric regions in Scyliorhinus and at the interstitial level in the two torpedo species. Studies with restriction enzymes (RE) have just been started in selachians, employing ALU I and HIND III in Scyliorhinus stellaris. The former digests the whole chromosome except the telomeric regions, revealing patterns similar to the C‐bands. The latter cuts the chromosomes into several interstitial regions, producing G‐bands. Other RE are being studied, which will allow identification in situ of qualitative differences in the various DNAs. Copyright © 1989 Wiley‐Liss, Inc., A Wiley Company

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.

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.

The molecular structure of chromatin during dogfish spermiogenesis was examined by electron microscopy after the dispersion of nuclei at low ionic strength. In early and late stages of differentiation (round and elongating spermatids), chromatin is globular, although basic nuclear proteins are different from those present in somatic nuclei. Three protein fractions are complexed with DNA in sperm nuclei. These fractions appear at the end of differentiation (elongated spermatids), subsequently undergoing a modification of their solubilization properties; only one protein fraction remains acid-soluble. Dispersed chromatin from sperm nuclei again shows a beads-on-a-string configuration both in the presence of the three specific sperm proteins and when the acid soluble fraction is extracted. Variations of the mean diameter of chromatin subunits during spermiogenesis appear rather limited compared to extensive modifications of chromatin superstructures.

Acid extracts of intestine from the dogfish Scyliorhinus canicula and Squalus acanthius were purified by gel filtration, ion exchange chromatography, and reversed-phase HPLC. In radioimmunoassays, VIP-like material from both species of dogfish cross reacted with N-terminal, but not C-terminal antisera. Like porcine VIP, both Scyliorhinus and Squalus VIP were stimulants of exocrine pancreatic secretion in the turkey. The time course of the responses to dogfish VIP were, however, different from that seen with porcine VIP. The present study has developed methods for the isolation of VIP-like peptides from elasmobranchs and has demonstrated that elasmobranch VIP differs from Porcine VIP in the C-terminal region, and that these differences may affect biological activity.

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.

SUMMARY Ovaries of dogfish were separated into their component tissues and incubated separately with [4-14C]dehydroepiandrosterone and androstenedione. Production of Δ4-3-oxosteroids from the former was localized in the follicular membrane, in the post-ovulatory corpora lutea and in the egg yolk. Reduction of androstenedione to testosterone was higher in corpora lutea than in corpora atretica and higher in follicular membranes and yolks taken from ripe follicles than in those taken from atretic eggs. Production of oestradiol-17β from androstenedione was limited to the follicular membranes of ripe follicles and to the ovarian stroma; oestrone production was demonstrated, additionally, in corpora atretica and their membranes. There was no indication of oestriol formation.

The effect of temperature on the CO 2 transport in the blood of some elasmobranchs ( Scyliorhinus, Mustelus, Torpedo ) was studied in the range of 9 to 25°C and at CO 2 tensions from 2 to 10 torr. The relative change in total CO 2 of whole blood was 2.5% per °C and that of the chemically bound CO 2 in true plasma4 % per °C. The log P CO 2 -pH lines shifted to a lower pH when the temperature was increased. The buffer capacity of true plasma was 10 meq/1 and per pH unit and that of separated plasma 4.2 meq/1 and per pH unit. These values were not affected by temperature. The buffer capacity of 1 g hemoglobin was 0.19 meq/1 pH unit. The molal heat of ionization was 7700 cal/mol. Human blood diluted to the same red cell volume displayed the same relationships between P CO 2 , C CO 2 and pH as dogfish blood. It is concluded that most of the CO 2 transport differences between man and dogfish are due to the lower concentration of the buffer proteins in dogfish rather than to different specific properties of the hemoglobin in dogfish and man.

A light stimulus, focused on the head of the dogfish shark ( Scyliorhinus caniculus ) over the end vesicle of the epiphysis cerebri (pineal organ), elicits a positive slow wave accompanied by inhibition of spike activity which was recorded from the cut end of the epiphyseal stalk. A stimulus of4.3 × 10 −4 lm/m 2 was sufficient to alter the on-going neural activity. From threshold to approximately 3 log units above threshold, there was good correlation between the amplitude of the slow potential and the inhibition of spikes. Further increases in the intensity of the stimulus did not elicit larger positive waves but greatly prolonged the duration of the inhibition of spikes. The observations can be best interpreted if the slow potentials arise from the ganglion cells and represent the summated inhibitory postsynaptic potentials transmitted electronically to the recording electrode. The spectral sensitivity of the epiphysis and the lateral eyes peak at 500 nm.