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1. A histochemical study has been made of alkaline phosphatase in the endoskeleton of dogfish embryos of 18-115 mm. 2. The distribution of phosphatase is compared with that of insoluble calcium salts. 3. Phosphatase was first noted in the chondrocytes and perichondrium at 47 mm. and in the cartilage matrix at 58 mm. 4. Calcification occurred first in the neural plates at 58 mm. and in the skull at 74 mm. No calcification was observed in zones devoid of extracellular phosphatase. 5. As the intensity of calcification increased the amount of phosphatase tended to drop. 6. It is concluded that in elasmobranchs, as in higher animals, extracellular phosphatase is an essential precursor of calcification.

In a former paper, descriptive of the type remains of Polacanthvs Foxii , some account was given of its dermal armour, but the description was unavoidably very incomplete, owing to the extremely fragmentary state of the parts originally composing it. Broken up by its discoverer into pieces small enough for convenient stowage and transport in bags from the cliffs to the village of Brighstone, two-and a-half miles distant, and then uncared for during fifteen years, the great dorsal shield, when after Mr. Fox’s death his collection was acquired by the British Museum, was represented by several hundreds of disconnected pieces, many of these being of less size than one cubic inch. It was also evident that many had been lost. In this mutilated condition the reconstruction of the shield appeared hopeless, but at length, under the guidance of the heads of the Palæontological Department, this has been accomplished by Mr. Hall and Mr. Barlow (“Masons”), who brought to the task a painstaking perseverance and skill worthy of the highest praise. Although now, doubtless, much less complete than when laid bare in the cliff by Mr. Fox, the reconstruction (which has consisted strictly in a faithful reunion of the disconnected scattered fragments) renders very intelligible the discoverer’s first impression, viz., that “he had before him the carapace of a gigantic turtle,” and it confirms his opinion of the position of the shield, viz., that it covered the rump and loins. The dimensions of the shield, given by Mr. Fox in a MS. note, 3 feet 3 inches by 3 feet, were taken roughly in the cliff before the shield was broken up. In its restored condition its breadth is 108 centims. in front, 105 centims. at its middle, and 48 centims. posteriorly, and its length is 90 centims. The relation of the shield to the pelvic bones makes it evident that the carcass was lying on its belly when it sank into the ooze, and that the shield was later crushed down upon the endoskeleton and flattened out.

Some morphological terms and characters of Chironomidae are discussed. The proposed terminology of the head chaetotaxy is more in accordance with that of other Diptera. The term flagellomere is preferred instead of flagellar segment. The morphology and terminology of tentorium, cibarial pump, maxillary palp, ocelli, and thorax including humeral pit are given special attention. Suggested terminology for the male hypopygium is as follows: gonocoxite and gonostylus for the major genital claspers, volsellae (consisting of claspette and endomere) for the appendices, phallapodeme, sternapodeme, and coxapodeme for the endoskeleton and aedeagal lobe for the "Dritte Spange". The term seta is preferred to such terms as hair, bristle, etc. It is suggested that in the larvae the name premandible be retained for the moment. There seems to be strong evidence for applying the term mentum instead of "hypostomial plate", "hypochilum", or "labial plate". The mentum seems to consist of two plates for which the terms ventromentum and dorsomentum are proposed. The "paralabial plates" are parts of the ventromentum and can be termed ventromental plates. A more correct name for the "glossa" seems to be ligula.

I am indebted to the liberality of Professor Edw. Forbes for many valuable specimens of fossil fishes, procured by Capt. Graves from the Lebanon range; and amongst the number, for the subject of the present memoir, one of the most interesting and remarkable ichthyolites ever brought to light by palaeontological research. The cases of the discovery of fishes belonging to the placoid order, in a condition at all approaching to completeness, are exceedingly rare. The destructible nature of the endoskeleton, and the loose attachment of its component members, attest the probability that decomposition would complete its work ere these records could be engrossed in imperishable characters. That this order was nevertheless extensively represented from the earliest fossiliferous period to the present time, is manifest from the frequent occurrence of the palatal tritores, teeth, and defensive fin bones of the Cestracionts, Hybodonts, and Squales; and of the dental apparatus, caudal weapons, and dermal tubercles of the Rays.

(1) A functional and comparative study has been made of the jaw mechanisms of representatives of the major classes of arthropods, covering, where appropriate, the whole endoskeletal systems of the head and the form and function of other mouth parts, hypopharynx, etc. (2) Mandibles are developed embryologically, and presumably phylogenetically also, in one or other of two ways. Type A, in which the biting structures are developed from a proximal endite or gnathobase (Crustacea, Chelicerata), and type B, in which the mandible is developed from a whole limb, the tip of which and not the base is used for gnathal purposes (Onychophora, Myriapoda, Hexapoda). (3) Two types of movement typical of the more primitive ambulatory trunk limbs have been exploited in mandibular evolution. Type I mandibular movement uses the promotor-remotor swing of an ambulatory or swimming coxa on the body, but the axis of swing may be shifted in various ways (Crustacea, Thysanura), and type II mandibular movement uses the prehensile action in the transverse plane of a coxa or coxa and telopodite. Type II is found in Myriapoda, where segmentation of the whole-limb mandible is essential, and direct transverse gnathobasic biting is employed by Limulus. Mandibles of types I and II appear to have evolved independently in the named examples. (4) The more primitive examples of type II mandibles suit fine food feeding and the scratching of food surfaces. The gape is small, biting, if any, is weak, and added hydraulic efficiencies enable fine particles to be sucked up by terrestrial types (Chirocephalus,Hemimysis,Paranaspides,Petrobius). (5) Biting in the transverse plane is not a primitive attribute of the Arthropoda outside the Chelicerata and certain Myriapoda. In the more primitive Crustacea and Hexapoda transverse biting is absent and there is little basic adduction and abduction. Transverse muscles primarily serve promotor-remotor rolling movements. No example has been found of a so-called monocondylic mandible of a crustacean or of a hexapod which exhibits freedom of movement in all directions from this point and a basic power of transverse adduction, whether or not the mandible possesses a formed dorsal articulation. (6) Strong biting in the transverse plane suiting hard or large food is a repeated end term in arthropodan evolution. The examples considered are: some Decapoda, Peracarida, Pterygota, Diplopoda and Symphyla. Adduction in the transverse plane is mechanically simple, but abduction presents great problems, hitherto not appreciated, which have had to be resolved by every group of animals attempting to evolve such mandibles. The resolutions of the difficulty are various, mutually exclusive, and independently evolved by mandibles of all types. (7) The feeding mechanism ofLimulusis described. The jaw mechanisms ofLimulusand of Crustacea are fundamentally different and have probably been evolved in independence. (8) The validity of the evidence for the existence of a pre-coxal segment in Xiphosura needs reconsideration. (9) The rolling whole-limb mandibles ofPetrobiusarenot far removed from a central type which could have given rise to the various mandibles occurring throughout the Hexapoda. It is shown in some detail how this mechanism is parallel to but different from that of the rolling gnathobasic mandibles of the more primitive Crustacea. Differences between the mandibles of Hexapoda and Crustacea concern mandibular form, musculature, movement and derivation; the head endoskeleton, and the form and movements of maxilla 1 are also different. The superficial resemblances are considered to be due to convergence between mandibles of unlike origin which utilize the same type of movement of an ambulatory limb. (10) Present-day animals show how thePetrobius-type of jaw mechanism could have given rise to (i) the strong transverse biting of the Lepismatidae and Pterygota with loss of hydraulic efficiency of the Petrobius type and to (ii) a further development of the rolling movement, together with protrusibility of mandibles, which has been made possible by entognathy in the Apterygota. These two trends are mutually exclusive. (11) Entognathy is a condition permitting great proximal mobility of the mandible and hence confers the powers of mandibular protrusion which are absent in strong closely articulated mandibles. Entognathy in essentially similar form, but differing in details, has been evolved in Onychophora, Chilopoda, Pauropoda, Collembola, Diplura and Protura. The ‘Entognatha’ is not considered to be a valid taxonomic group but one of convergence. (12) A basic pattern of: mandibular structure, musculature, movements, associated head endoskeleton, and of the structure and movements of maxilla 1 is recognizable throughout the less specialized Pterygota, Thysanura, Collembola and Diplura, so linking these groups together by characters having nothing to do with the possession of three pairs of legs. This basic pattern of mandible and maxilla 1 is not found in the Myriapoda. (13) A unified system of skeletal tendons and apodemes exists within the Arthropoda which has hitherto been imperfectly described. Anterior and posterior tentorial apodemes are present throughout the less specialized of the Hexapoda in essentially similar form. The segmental tendon system, present embryologically in all body segments in many animals, occurs in the adult hexapod head except where strong transverse biting has been evolved, and its presence then is consequently not required. Hexapod-like tentorial apodemes are absent in Crustacea, but homologous anterior tentorial apodemes are present in Myriapoda where their mobility is enhanced. Rigidity of tentorial apodemes is found in hexapods where strong transverse biting has been evolved (Pterygota). (14) The details of the feeding mechanism of a chilopod are described. The mandibular mechanism has clearly been derived from the same basic transversely moving mandibles of the type seen in Diplopoda and Symphyla, but modified by the development of entognathy to give a highly specialized mechanism suiting carnivorous feeding and crevice living, and not found in any other group. (15) The Chilopoda, Diplopoda and Symphyla all appear to have obtained direct transverse biting without any preliminary rolling mandible such as seen in Thysanura, but segmentation of their mandibles is essential. All have used the mobility of the anterior tentorial apodemes to provide (Diplopoda) or enhance (Symphyla and Chilopoda) the abductor force which opens the jaws. The differences between the mandibular mechanisms of Chilopoda, Diplopoda and Symphyla indicate independent evolution from a common type and no one of these three classes could readily give rise to the mandibular mechanisms present in either of the other two. The term Myriapoda, indicating affinity between Chilopoda, Diplopoda, Symphyla and Pauropoda deserves to be reinstated. (16) The symphylan mandibular mechanism, together with the structure and use of maxilla 1, the mobility of the anterior tentorial apodeme, and the presence of the myriapodan maxilla 1 salivary gland, are so entirely opposed both to the thysanuran condition and to the directions of evolutionary change seen in the Pterygota and entognathous Apterygota (whose basis appears to lie in the Thysanura) as to make the symphylan theory of insect origin untenable. (17) It is concluded that jaws have evolved independently in (i) the Chelicerata, (ii) the Crustacea and (iii) the Onychophora—Myriapoda—Hexapoda series. Within the latter the jaws in the Onychophora must have evolved very early, before much cephalization had taken place. The mandibular mechanisms of the Myriapoda and Hexapoda are so differ ent as to indicate that there can be no close connexion between these two groups of classes apart from a very distant common origin. The parallel evolution of jaws in arthropods must date from the earliest differentiation of the major classes. The Mandibulata cannot be regarded as a related group, but the term may serve to indicate a Grade of advancement. The bearing of these results on taxonomic systems is discussed.

Summary 1 The endites of the pedipalps form an apparatns for gripping the hair. 2 The pedipalpal endite has powerful adductors but shorter and weaker abductors. 3 Taking the musculature and curvature of the endites into consideration, it seems unlikely that the animal can release the hair. 4 The food appears to be scales and the secretions of epidermal glands scraped off the hair by the chelicerae. 5 The gut has virtually lost the lateral caeca of the more typical Sarcopti-formes, and shows no clearly differentiated post-colon. 6 The female reproductive system has developed a long median glandular common oviduct. 7 The female system shows the bursa copulatrix and receptaculum seminis typical of Tyroglyphoidea. 8 By loss of accessory glands the male reproductive system has come to resemble that of the female quite closely. 9 The posterior region of the suboesophageal ganglion mass is subdivided into a pair of lobes. Each lobe innervates legs III and IV, the genital valves and dorso-ventral muscles of its own side. 10 The muscles associated with movements of the gnathosoma on the podosoma are lost. 11 Development of lateral plates on the tectum of the gnathosoma and extensions of the epimera of leg I to articulate with the pedipalpal coxae render the gnathosoma immobile. 12 The adductor system of the legs is modified in that it has its origins not on the body wall or tendinous endoskeleton but on the epimera in the case of legs I and II and on the posterior end of the sternum or an internal projection of the body wall in the case of legs III and IV respectively.

A brief account and new restorations of the Scottish Middle Old Red Sandstone fish Rham phodopsis are given, based largely on new material from Edderton, Ross-shire. The Edderton material is of the species Rliamphodopsis threiplandi Watson, previously known only from A chanarras, Caithness. The known material of Rhamphodopsis trispinatus Watson, from Moray Firth and Cromarty nodule beds, has been restudied for comparative purposes, and notes are also given on some ptyctodonts from the Upper Devonian of Wildungen, Germany. New points in the structure of Rhamphodopsis concern mainly the sensory line system, jaws, cervical joint, and pelvic fins and associated structures. The occurrence of strong sexual dimorphism in the pelvic region is confirmed, and descriptions are given of the ‘claspers' in males, and of the large scale-bearing pelvic fins and their endoskeleton in females. Some consideration is given to the biology of ptyctodonts.

1. The ichneumonid parasite Gelis corruptor is trimorphic in the development of wings: females are invariably apterous; males may be either macropterous or micropterous. 2. Females show no trace of wing-buds in the pupa and are without wing-disks in the late larval stage. The female apteryis a sex-limited character and is of genetic origin. 3. All male larvae have wing-disks and are potentially fully winged males. On a host providing adequate nourishment, the male larva develops into the macropterous form; on a host providing meagre nourishment, it develops into the micropterous form. Eggs or young larvae transferred from a small to a large host develop into macropterous males; larvae removed from large hosts before they have finished feeding develop into micropterous males. The dimorphism of the male sex is therefore controlled by the host viewed as a quantity of food. 4. The two forms of males differ not only in the development of the wings but also in the structure of the thorax, the size of the ocelli, the form of the endoskeleton, and the development, innervation, and tracheal supply of the thoracic muscles. 5. The trimorphism is strict, since all females are apterous and (with the exception of one abnormal specimen) all the males examined belong without intermediates to either the macropterous or the micropterous form. 6. The principal differences observed between the three forms all appear to be bound up with the condition of the wings. How the development of this complex of characters is organized, particularly in the two forms of males, presents an interesting problem of morphogenesis.

Morphology of adult female and male reproductive systems of Strumeta tryoni (Froggatt) is described and figured. Growth changes in adult male reproductive endoskeleton are described under differing conditions of temperature and light intensity. For the environmental conditions studied, physiological age was correlated with size of the male reproductive endoskeleton and a method for distinguishing teneral from sexually mature adults is given.

The ultrastructure of the fowl spermatozoon differs in several ways from that of the mammalian spermatozoon, and the probable implications of the findings for the difficult problem of storing fowl semen in vitro are discussed. The acrosome has a simpler structure than in the mammal and does not spread down over the membrane of the head. Greater structural differences occur in the tail region, the middle-piece of which is particularly prone to deteriorate in vitro. The eleven axial (tail) fibres arise from a centriolar complex in the neck region of the spermatozoon; at this level, and more distally in the wall of the distal centriole, they resemble microtubules in cross-section. The nine outer ones show the triplet tubule structure typical of cell centrioles. The complex ‘endoskeleton’ of segmented columns in the neck, and outermost coarse fibres in the middle-piece and principal-piece of the tail, are absent in the fowl. In the distal part of the middle-piece the tail fibres separate; here and in the principal-piece they show the typical doublet structure seen in the tail of mammalian spermatozoa, cilia and flagella. The principal-piece of the fowl spermatozoon is composed solely of a continuous sheath of amorphous material surrounding the eleven axial fibres; the sheath is absent from the distal end of the tail. In contrast with the situation in the mammal, no segmentation of this material is evident and no continuous lateral columns are present in the tail.

Grafting experiments on H. viridis were performed to determine whether the epitheliomuscular cells of the epidermis and the digestive cells of the gastrodermis normally moved independently. In one set of experiments testes were employed as an epidermal marker and the border between algae-laden and algae-depleted digestive cells as a gastrodermal marker. Testes were often observed to move proximally at a faster rate than the border. In another set of experiments composite animals were made from normal and C 14 -labeled animals. Autoradiograms often showed that the epitheliomuscular cells moved proximally faster than the digestive cells. Moreover, in H. pseudoligactis , the epitheliomuscular cells had more mitotic figures per unit area than the digestive cells. This independent movement and growth makes it impossible to imagine the mesoglea as a “cement” holding the two cell layers together. Mesogleas were isolated in order to see if they had properties consistent with their being a substratum for cell movement. They were found to be elastic and tough and to retain the cylindrical shape of the organism even in the absence of cells. A collagen-like protein is present in the mesoglea as shown by the conditions for its extraction, by the behavior of its heat-denatured products on disc electrophoresis, and by the presence of hydroxylysine and hydroxyproline. The role of mesoglea as an endoskeleton in Hydra is discussed.

The author describes the large dorsal shield, which has been recently restored and now exhibits the grouping of the keeled and tuberculated fragments, which in their disconnected and scattered condition had formerly been regarded as portions of separate scutes. This unique specimen shows Polacanthus to have possessed a more complete dermal armature than any other Dinosaur yet described.