bluuebunny/crossref_metadata_2025 huggingface dataset:
“Proboscis pores” in Craniate Vertebrates, a Suggestion concerning the Premandibular Somites and Hypophysis.
Authors: Goodrich Edwin S.
Published: April 2021

There is in Amphioxus on the roof of the buccal cavity a deep pit known as Hatschek’s pit, from its discoverer. Its blind, inner end extends upwards to the right of the notochord, while the lining epithelium is continuous at the opening of the pit with the areas of thickened ciliated epithelium which spread over the roof and sides of the buccal cavity. This ciliated organ is the wheel-organ of Johannes Muller, and was shown by him to drive a current of water and food-particles into the mouth. Van Wijhe (14) has since given a detailed account of its structure. An unpaired dorsal region extends backwards so as to surround the opening of the pit, then divides into right and left tracts. The two branches run towards the velum and then down the sides of the buccal cavity, but do not meet ventrally. As shown in Text-fig. 1, finger-shaped tracts extend forwards on the inner surface of the oral hood. These structures become more complicated in older specimens. The deeply staining epithelium of which Muller′s organ is composed is formed of very closely packed, narrow columnar cells, whose nuclei form several layers, and whose outer ends bear each one cilium. Good figures of these cells have been given by Langerhans (8).
The Segregation of the Germ-cells in Tricho-gramma evanescens.
Authors: Gaieiiby J. Brouté
Published: April 2021

In a previous paper (4) I described a number of stages in the development of Tricliogrannna evanescens, but at that time I was unable to follow out the segregation of the germ-cells. Since then I have collected more material, and in this paper I am able to describe the missing stages.
The Cytoplasmic Inclusions of the Germ-Cells. PART III. The Spermatogenesis Of Some Other Pulmonates.1
Authors: Gatenby J. Brouté
Published: April 2021

Eight species of Pulmonates have been carefully studied, and certain stages of four more species examined. A new set of plasmatic bodies, the post-nuclear granules have been described. The P.N. granules differ from the mitochondria in their staining affinities, but resemble them in size. The P.N. granules ultimately form a plate at the rear of the spermatid nucleus. This plate, at first large, gradually shrinks synchronously with the shrinkage stages in the nucleus. The P.N. granules appeal’ to become non-staining during the maturation division, but it is not known whether more intense chromatization of the material (Benda) might not bring them into evidence. The mitochondria of the Pulmonates so far studied are of the same general type. On p. 239 twelve conclusions are given with regard to the mitochondria both of Pulmonates and of other forms. The chondrioplasts of all the Pulmonates dealt with have been fully examined. The chondrioplasts of different genera and often of different species tend to differ a little in shape aud size. The chondrioplasts during the prophases of the first maturation karyokinesis lose a great deal of their staining affinity. In many cases during the metaphase, anaphase, and telophase it cannot be demonstrated without specially heavy chromatization and staining. During these periods it changes, in its chemical constitution. The centrosome is responsible for the sorting out of the chondrioplasts into two equal groups at the prophase of division. The batonette is not divided by fission, but goes to the daughter-cell complete. After the final maturation division is over, the chondrioplast rod resumes its lost staining affinity. The chondrioplast batonettes do not take direct part in the formation of the spindle. The micromitochondria have been thoroughly re-examined with iron hæmatoxylin and Benda’s method. Their presence is confirmed by all tests that could be made. They seem to differ in staining capacity from the macromitochondria. The presence of micromitochondria in other forms is doubtful, because the cells are so small as to make proper examination impossible. Micromitochondria appear to be present in Limax agrestis and in H. rufescens. The mitochondria, during the maturation divisions, stain less heavily, and often become larger. The latter fact could not be demonstrated in every case. On p. 248 I have stated the periods during which the mitochondria, appear to alter in staining affinity and resistance to certain fixatives. The affinities of the several species have been discussed on the basis of their cytoplasmic bodies. Tables of staining and fixing effects have been given. From the three papers already published on the “Cytoplasmic Inclusions “it will be seen that strong evidence is being collected against the view that the mitochondria take any part in the transmission of the “factors of heredity.”
Ecdysis in a Teleostean Fish, Agriopus
Authors: Gilchrist J. D. F.
Published: April 2021

Agriopus is a well-known fish of the Southern Hemisphere, and is recorded from South America, South Africa and Australia. On account of its striking appearance it attracted the attention of early travellers, and is first mentioned by Block under the name of Coryphæna torva. It has a mane-like dorsal fin and a long vertical forehead, from which it derives its local name “Horse-fish.” A further characteristic, mentioned by all observers, is its soft, thick skin devoid of scales. This was specially noted by Cuvier and Valenciennes, who describe the skin of A. tor vus as “épaisse et lisse comme un cuir’ bien préparé, sans aucune apparence d’écailles.” They add that, among the specimens procured, there were some in w’hich the skin was quite brown and raised in small wart-like prominences, so well marked as to suggest that these individuals represented a different species, though otherwise not dissimilar.
On the Blood-Vase alar System of the Earthworm Pheretima, and the Course of the Circulation in Earthworms
Authors: Narayan Bahl Karm
Published: April 2021

The typical arrangement of the blood-system in Phere-tima occurs in the region of the body behind the fourteenth segment, the first fourteen segments forming the cephalized region. The main longitudinal trunks are the same as in Lumbricus, except that the lateral neurals are absent as in Allolobophora. The dorsal vessel receives two pairs of dorso-intestinals and one pair of commissurals in each segment behind the cephalized region. The intestinal blood-plexus is both an external and an internal one, and three regions can easily be distinguished. The first is internal, and extends from the fourteenth to the twenty-sixth segment ; the second is both external and internal, is co existent with the typhlosole, and extends over the larger part of the gut ; and the third is only external, and is confined to the rectal or post-typhlosolar part of the gut (last twenty-three to twenty-six segments). The commissural vessel of Pheretima is a compound vessel, and represents both the ‘dorso-sous-nervien ’ of Lumbricus and theintestino-tegumentary of Megascolex. The capillaries of the integument are not like these of Lum-bricus but like these of Moniligaster, and there is a close ’parallelism ’ between an ‘artery ’and a ‘ vein ’in the body-wall, in which the two pass into each other through a number of capillary loops. There are four pairs of ‘hearts’ which connect the dorsal with the ventral vessel, and five pairs which supply blood directly to the various organs in the cephalized region. There are two pairs of non-contractile ‘anterior loops’ connecting the lateral oesophageals with the supra-intestinals, these loops being the counterpart of the connexions of the lateral oesophageals with the dorsal and the parietal in the tenth and twelfth segments respectively of Lumbricus. The subneural vessel is absent in the first fourteen segments, and is continuous with the lateral oesophageals of the anterior region. As regards the course of circulation of the blood, the chief fact is that the dorsal vessel is wholly ‘venous’ behind the ‘hearts’ and wholly ‘arterial ’ in the region of the ‘hearts ’ and in front (the whole of the cephalized region). The examination of valves and experiments by cutting and pinching the blood-vessels in Pheretima confirm the results of Johnstone for Lumbricus as regards the course of blood in dorso-intestinals and commissurals and make Bourne’s theory untenable. The ventral vessel is the arterial trunk throughout, while the venous function of the dorsal and subneural behind is taken up by the lateral oesophageals in the cephalized region. The thin-walled and non-contractile ‘loops’ of the tenth and eleventh segments must be distinguished from the thick walled and contractile ‘hearts’ of the other cephalized segments, the ‘loops ’ being the channels for conveying blood from the lateral oesophageals to the supra-intestinals.
Studies in Dedifferentiation.: II. Dedifferentiation and resorption in Perophora
Authors: Huxley Julian S.
Published: April 2021

The social Ascidian Perophora viridis may dedifferentiate in either of two distinct ways, or by a mixed method: (a) by reduction to a spheroidal mass, as in Clavellina; (b) by incipient reduction as in (a), but followed by total resorption into the stolon, which may grow during the process. Resorption is due to the migration of the individual cells out of the tissues into the haemocoel. In certain conditions the zooid maintains itself, in spite of food not being provided, at its original size and in perfect health. This it does by resorbing the stolon. Experiments with dilute solutions of KCN show that resorption of the zooid occurs in slightly unfavourable conditions, which affect the sensitive zooid, more than the less highlyorganized stolon. The results are to be explained as follows: (a) In the competition between zooid and stolon the zooid normally is dominant because metabolic processes take place at a greater rate in it than in the stolon. The stolon is therefore starved at the expense of the zooid, (b) The zooid is more susceptible than the stolon to toxic agencies, (c) In low concentrations of such agencies it is therefore affected while the stolon is not. (d) As a result it begins to dedifferentiate. Dedifferentiation is here accompanied by the migration of the cells out of the tissues, (e) The speed of its metabolic processes is now no longer greater than that of the stolon’s. It is therefore now starved at the expense of the stolon, (f) Any cells migrating out of the tissues are removed by the normal circulation, by the stoloncirculation (irregular pulsation of the stolon), or by utilization as food by the stolon. As in chemical reactions where the end-products are removed, the reaction thus runs to its limit, i. e. to complete resorption of the zooid. Stopping the circulation by means of KC1 results in dedifferentiation accompanied by a much smaller degree of resorption. At low temperatures (about 5° C.) some dedifferentiation occurs; but there is very little resorption, apparently owing to the cessation or slowing of the heart-beat. Partial dedifferentiation is recorded in Amaroucium and Botryllus. The significance for general biological problems of dominance due to high rate of metabolism, of differential susceptibility and of dedifferentiation, is discussed. The similarity of certain psychological and neurological phenomena is noted (mental regression, alteration of spinal reflexes when freed from cerebral control, &c.).
Surface Tension and Cell-Division
Authors: Gray J.
Published: April 2021

The series of changes which a dividing cell exhibits has long suggested to biologists that surface tension plays a dominating rôle in the process of cleavage. Without exception, theories based on this suggestion have postulated regions of differential tension on the cell-surface ; the surface tension at the equator of the cell has been held to be either higher or lower than that at the polar regions of the cell. Such theories have proved of but little value as a means of further investigation, since there is no apparent means of determining how such a state of affairs could arise, nor is there any apparent differentiation in the microscopical structure near the equator of the cellsurface.
The Formation of the Peritrophic Membrane in Insects, with Special Reference to the Larvae of Mosquitoes
Authors: Wigglesworth V. B.
Published: April 2021

In the larvae of mosquitoes (Anopheles, Culex, and Aedes) the secretion from the cells of the cardia, in the proventriculus, is drawn through an annular press and thereby moulded to form the peritrophic membrane. The mechanism of this press has been described in detail.

It seems probable that, throughout the Diptera, the peritrophic membrane is formed by similar mechanisms. Figures are given of those in the larvae of S ciar a (Cecedomyidae), Rhyphus (Rhyphidae), and Telmatoscopus (Psycho-didae).

Analogous structures (a zone of secreting cells in connexion with an annular press) have been found in most of the main orders of insects, as follows : Hymenoptera [adult of Bombus and Apis and the larva of a saw-fly (Tenthredinidae)] ; Coleóptera [larva of the mealworm (Tenebrio molitor) and the adult of Coccinella]; Lepidoptera [larvae of Cheima - bacche fagella (Oecophoridae), Sitotroga cerealella (Gelechiadae) and Ephestia kuhniella (Pyralidae)] ; Aphaniptera (larva of Ceratophyllus wickhami); Iso-ptera ; Neuroptera (adult of Hemerobius); Odonata (larva of Aeschna); Orthoptera (Blatella germánica); and Dermaptera.

In every case, in addition to its function as a press, the so-called ‘oesophageal valve’ was found to act not as a valve but as a sphincter.

In the honey-bee (Apis), the larva of the dragon-fly (Aeschna), and possibly in other insects, indefinite membranes are shed off by the cells farther back in the mid-gut, and added to those produced in the annular press.

In all the insects examined, chitin formed the basis of the peritrophic membrane.

The observations recorded give a coherent significance to much of the previous work on the subject, which, before, appeared contradictory.
On the behaviour and structure of cells of Helix aspersa in aseptic and non-aseptic tissue culture
Authors: Gatenby J. Brontë , Hill Joyce O. , Macdougald T. J.
Published: April 2021

In a previous paper in this Journal (16), the two senior authors have given some account of the behaviour of small pieces of the wall of the mantle cavity of Helix aspersa, kept in Hédon-Fleig saline. Since our last communication a considerable amount of work has been done by two of us. (J. C. H. and T. J. M.) on this cultivation in vitro, the main object of which has been to obtain aseptic growths. A more intensive study of various media has been made, and we have found it comparatively easy to obtain aseptic cultures, even in a room which could not be used expressly for this type of work.
The Life-History of Sacculina
Authors: Day J. H.
Published: April 2021

This paper contains a revised version of the life-history of Sacculina stressing certain points which have arisen as a result of work on the effects of the parasite on its host.

From the statistical analysis of a year’s samples of an infected crab population it is concluded; first, that crabs may be infected at any age; secondly, that the developmental sequences in the life-history of the parasite are dependent not on the season but possibly on the phases of the host; thirdly, that the internal development of the parasite lasts nine months, and that the first batches of larvae appear three months later.

Two separate experiments showed that the évagination of the parasite does not take place at an ecdysis of its host.

It is suggested that an anomalous group of highly modified male crabs without externae but containing living parasitic roots are ‘scarred crabs’ that have moulted; further, that such modified crabs will in time regenerate externae. Experimental and histological evidence supports this suggestion, but it is not held that the theory of regeneration is completely proved.

An account is given of the effects of Sacculina on the secondary sexual characters of Portunus holsatus. Only male crabs are dealt with. It is shown: (a) that various degrees of modification are possible; (i>) that the percentage of infection increases among large crabs; (c) that the smaller the crab the greater the liability to maximum modification; (d) that the maximum amount of modification which is possible decreases among larger crabs.
On the Post-embryonic Development of the Respiratory System of Dialeurodes dissimilis (Homoptera, Aleurodidae)
Authors: Roonwal M. L.
Published: April 2021

Accounts of the post-embryonic development of the tracheal system of any insect are extremely meagre. The development of the breathing-folds has not been studied in any of the Aleurodidae. The present account is concerned with the post-embryonic development of the respiratory system (the tracheal system and the breathing-folds) in the nymphs of Dialeurodes dissimilis Quaintance and Baker (Aleurodidae, Homoptera). The number of spiracles in all the nymphal instars is four (probably five in the first instar). They lie on the ventral surface of the nymphs but their exact position varies in the different instars. The third pair of spiracles is replaced by an entirely new one in the third instar. The spiracles, as studied in the pupa, are of a simple type and have no closing mechanism. The tracheal system consists fundamentally of paired ventral- and dorsal-longitudinal tracheal trunks, two dorsalcommissural tracheae, the spiracular and palisade tracheae, and the various branches of the main system. Growth of the tracheal system consists, on the whole, of arborescent branching from the main system, but there also occur some interesting changes of atrophy. All these changes are described in detail. The final number of tracheal branches (in the pupa) is constant, and is 156. There is a gradual shifting backwards of the tracheal system with reference to the body segments. Some of the tracheal branches which in the pupa are apparently homologous actually develop heterochronously. The structure and development of the breathing-folds is described and their function discussed.
The Cytoplasmic Inclusions in the Spermatogenesis of Man
Authors: Gatenby J. Bronte , Beams H. W.
Published: April 2021

The points which we have brought out in this paper are:The development of the acrosome from the Golgi apparatus, which has been figured for the first time during growth, and the stages of acrosome formation in the human.The almost complete break-up of the Golgi apparatus at dictyokinesis, and the late reassembly of the fragments apparently independently of the spermatid centrioles.The very probable presence of a neck granule apparatus as distinct from the head or proximal centriole (c1).The claim that the head centriole does not divide. The emergence of the flagellum from the proximal and distal centrioles jointly.The development of the post-nuclear cap in human spermatids.The apparent absence of any form of spiral body in the middle-piece.The different types of Golgi apparatus in the Sertoli and spermatogenic cells.The presence of a vacuole in the head of the spermatozoon.The remarkable ‘nutrient syncytium’ connected with the Sertoli cells.The accessory body in the cytoplasm.
The Development of the Adrenal Gland of the Mouse
Authors: Waring H.
Published: April 2021

The cortical anlage is constituted from the mesenchyme at about the 12th day of embryonic life. The medullary anlage is constituted at about the 13th day of embryonic life from the anlage of the sympathetic nervous system and lies closely adpressed to the cortical anlage. At about the 14th day sympatho-chromaffin elements migrate from the closely adpressed sympathetic nervous mass into the cortical anlage and form irregularly arranged ‘nests’ in its substance. Between 16 and 18 days of foetal life part of the cortical substance has differentiated by becoming less eosinophil and is destined to form the adult permanent cortex. By the day of birth the sympatho-chromaffin elements are concentrated at the centre of the gland and are beginning to metamorphose into medullary cells.

The undifferentiated eosinophil cortical tissue now forms a layer immediately outside the medulla and interlocking with the medullary tissue.

The less eosinophil tissue now shows the first distinct signs of the arrangement characteristic of the adult glomerular and fasciculate zones. After birth, in both sexes, the interlocking zone increases, attaining its maximum at about 21 days in the male but continuing to increase in the female, so that at about 25 days there is a distinct sex difference.

The three zones of the adult cortex are distinguishable in both sexes by 25 days—the glomerulosa, zona fasciculata, and zona reticularis.

The reticular zone is distinctly a product of the zona fasciculata and not of the interlocking eosinophil zone. At 30 days in the male degeneration of the interlocking zone has begun—in the female the zone is still increasing. The male reticular zone is now very clearly developed but that of the female has remained at the 25-days condition.At 35 days in the male degeneration of the interlocking zone has become well established. In the female this zone attains its maximum development at about this period.By 56 days in the male the degeneration of the interlocking zone is complete, leaving a connective tissue capsule between the medulla and the well-marked zona reticularis of the permanent cortex. (The female is not discussed beyond 35 days.)The interlocking zone of the adrenal of the mouse (X-zone of Miller) is shown to be probably homologous with the boundary zone of man and of the cat.
The Germinal Layers concerned in the Formation of the Alimentary Canal and Malpighian Tubules of Epbestia Kühniella (Lepidoptera)
Authors: Drummond Mabel
Published: April 2021

The mid-gut epithelium of Ephestia is derived from cephalic and caudal mesendoderm rudiments which are proliferated from the germ-band independently of the stomodaeal and proctodaeal invaginations. The oesophageal valve is formed by the backward growth from the blind end of the stomodaeum of six tubules, which later in a slightly altered form extend into the cavity of the mid-gut to form the valve of the larva. The stomodaeum and proctodaeum are purely ectodermal. The malpighian tubules are ectodermal.
Royal Microscopical Society
Authors: Glaisher James
Published: April 2021

The minutes of the preceding meeting were read and confirmed.
Nobert’s Test-Plate and Modern Microscopes
Authors: Stodder Charles
Published: April 2021

Every possessor of a first-class microscope wishes to know what his instrument is capable of doing. To the practical worker it is a matter of much importance, for when the utmost power of his instrument is exhausted he will know that it is a waste of time to endeavour to see more. One of the desirable and important properties of a microscope is the power to show or “resolve” very fine lines grouped together, e.g. the striation of the frustules* of the Diatomaceæ. For the purpose of testing the resolving power of the microscope, the lines ruled on glass by F. A. Nobert, of Barth, Pomerania, have long been admitted by experts as the best known test, not only in consequence of their exceeding fineness, but also because they are ruled to a known scale, and because they are so close that physicists have asserted that it is impossible that they ever can be seen, Nobert himself being in this category; and all trials of these plates, except those to be herein mentioned, have resulted in failures to resolve the finer lines of these plates.
Experiments on Young Salmon*
Authors: Mcintosh W. C.
Published: April 2021

Early in 1862, and in the winter of 1862-3, the development of numerous salmon ova was observed, and some experiments performed on the young fish. Unfortunately, these had to be laid aside in March, 1863, for more pressing engagements, with the intention of again resuming them on a favorable opportunity; but since this has not occurred, the results—such as they are—are now briefly narrated. I may likewise state that during the progress of the experiments much valuable advice was kindly given by Prof. Christison, some of whose experienced suggestions were not fully carried out, on account of the sudden interruption of the work.
Notes on some Rare British Polyzoa, with Descriptions of New Species
Authors: Norman Alfred Merle
Published: April 2021

The object of the following paper is to embrace a few notes upon some of the rarer of the British Polyzoa, and to describe several species new to science.
The Spermatheca of Loligo vulgaris: I. Structure of the Spermatheca and function of its Unicellular Glands
Authors: Oordt G. J. van
Published: April 2021

The structure of the spermatheca of Loligo vulgaris is described; it lies on the inner wall of the buccal membrane and within it large quantities of inactive spermatozoa are stored.

This inactivity of the spermatozoa within the spermatheca is attributed to the effect of the secretion of the goblet-cells, situated as unicellular glands on the inner wall of the spermatheca.

Inactive spermatozoa from the spermatheca become very active in sea-water, but are immobilized again after a few moments’ contact with the pulp of the spermatheca contents.

The hydrogen-ion concentration of the spermatheca contents is approximately 6-06; and, since spermatozoa become inactive in sea-water, the hydrogen-ion concentration of which is increased to this level, it seems probable that the inactivity of the spermatozoa within the spermatheca is due to the presence of hydrogen-ions.

The spermatheca is functionally comparable to the mammalian epididymis.
Abdominal appendages in the female and copula tory appendages in the male Asellus
Authors: Needham A. E.
Published: April 2021

1. In the female Asellus aquaticus it is the first pair of pleopods which is missing and not the second pair, as was usually held. This condition is the result of an inhibition on the development of the last thoracic and first abdominal segments in later brood-pouch stages, an inhibition which is only temporary in the last thoracic segment and in the first abdominal segment of the male.

2. The resemblance between the second abdominal appendages in the female and the first pair of the male is therefore purely convergent.

3. The strong probability that the same condition holds throughout the sub- order Asellota is supported by a comparison of adult morphology, and should be verified by embryological study. It is more usual in Crustacea for appendages to be lost at the end than in the middle of a series.

4. The structure of the copulatory apparatus of the adult male Asellus is extremely complex, and apparently closely adapted to its mode of function. In contrast the female apparatus is of the simplest.

5. Points of evolutionary and genetical interest are raised by the condition of these appendages in the two sexes.
Spolia Bermudiana II. The Ciliary Feeding Mechanism of Tornaria
Authors: Garstang Walter
Published: April 2021

During my first visit to Bermuda in February 1935, large Tornaria and Auricularia frequently occurred in the plankton, so that I hoped, in the intervals of other work, to be able to compare the feeding processes in the two types. For some unknown reason, however, ciliary action had always stopped in the large Auricularia nudibranchiata when examined in the laboratory, while Tornaria, on the other hand, was usually fresh and lively, and I made a preliminary study of its behaviour. On my second visit in June-July of this year (1938) both types were scarce, and I could make no further progress with the problem. It seems desirable, therefore, to publish my notes on the feeding of Tornaria, without waiting longer for the opportunity of a comparative study.
The Structure of the Ovary and the formation of the Corpus Luteum in Hoplodactylus Maculatus, Gray.
Authors: Boyd Mary M. M.
Published: April 2021

The structure of the ovary, including stages in the ripening of the oocytes, is described. A prolonged diplotene stage with ‘lamp-brush ‘chromosomes is shown to occur in reptiles, as in other classes of vertebrates with large yolky eggs.

The striated layer of the egg membrane is shown to be composed of the same cuticular substance as the zona pellucida. A follicular epithelium composed of three types of cells, later reduced to a single layer of small cells, agreeing with Loyez’s observations, is described.

A discontinuous theca interna, comparable with that of mammalia, is noted outside the membrana propria of the nearly ripe oocyte.

A thin, soft, fibrous shell membrane is formed round the uterine egg and polyspermy occurs. The latebra, and the male and female pronuclei in apposition, are described.

The corpus luteum is shown to consist of luteal cells invested by fibroblasts from the theca externa. Septa of fibroblasts arb also present, but no blood-vessels. The theca is rich in capillaries. The theca interna plays no part in the development of the corpus luteum. A lipoid secretion, which may be of physiological importance, is formed in it. It is compared with that in Monotremes and Marsupials.
The Significance of ‘Chromatic Droplets’ in the Growth of Insects
Authors: Wigglesworth V. B.
Published: April 2021

From a review of the literature, and from observations on Rhodnius prolixus, it is concluded that the ‘chromatic droplets’ which appear in the epidermis during the moulting and metamorphosis of insects are formed from the dissolution of entire nuclei; nuclei that have become superfluous, either because they belong to specialized larval structures that are being discarded, or because the exuberance of cell division has led to their production in greater numbers than are needed.
Primary Sex-Phases in Ostrea edulis.
Authors: A. Cole H.
Published: April 2021

1. It is only under the most favourable conditions that oysters (Ostrea edulis) mature in the first sexual phase in the same season as that in which they attach themselves. During this initial phase the oyster functions as a male.

2. Normally the first male phase is experienced on British beds in the summer following that in which the oyster attaches itself and is rapidly followed by the first female phase, the oocytes developing on the walls of the follicles while spermatogenesis proceeds in the lumina.

3. In favourable seasons about a third of a population of one-year-old oysters will spawn as females. In unfavourable years only a few of the heaviest oysters spawn. Following female spawning the second male phase is rapidly assumed.

4. The second male phase is followed by the second female phase, the oocytes developing while spermatogenesis is in progress. Emission of sperm may be continued up to within a few days of egg-spawning. If a male phase is reached towards the close of the season it is followed by a resting phase, without spermatogenesis or large oocytes in the gonad, which persists throughout the winter. Similar resting phases may occur during the summer if environmental conditions are unfavourable.

5. Every two-year-old oyster functions as a female in a favourable season, and thereafter under normal conditions passes through at least two sex-phases each season, functioning both as a male and as a female. Evidence is adduced to show that in populations of adult oysters on British beds 100 per cent, female functioning occurs in favourable seasons.

6. Gonad development is arrested from approximately the end of October until the beginning of April while the water temperature is below about 10° C. Oysters may winter in almost any sex-phase, but spermatogenesis does not occur, although ripe sperm morulae may be carried over from one season to the next. Egg development is arrested during the winter months.

7. Oysters which winter in a transitional phase between a male and a female phase may mature as pure females early in the following summer without any recrudescence of spermatogenesis. There is at this time, therefore, a high proportion of ripe females in the population.

8. Oysters which winter in a dormant male condition mature as good males early in the following season and spawn as females later in the summer. Female spawners may therefore be divided roughly into two groups—early and late spawners—and individual oysters tend to remain in the same group in successive years.

9. Breakdown and absorption of large eggs by phagocytes has been found to occur occasionally during the winter, but the circumstances in which this takes place are not known.
Development of the Mesonephros in a Teleostean—Thynnichthys sandkhol
Authors: Moghe M. A.
Published: April 2021

The development of the mesonephros in teleostean fishes has been the subject of investigation by a large number of workers. Among these may be mentioned Rosenberg (1875), Goette (1875), Fürbringer (1878), Nussbaum (1878), Emery (1882), Hoffmann (1886), Felix (1897), and more recently Maschkowzeff (1934).
Notes on Certain Fresh-Water Species of Diatomaceæ
Authors: Donkin A. S.
Published: April 2021

The late Professor Smith, in referring to the genus Epi- themia in his ‘Synopsis of the British Diatomaceæ ‘(vol. i, p. 11), observes that “this genus, as its name implies, is characterised by the adherence of its frustules to Aigre of larger growth. This character is true of most of the species, and even where not strictly applicable, as in E. gibba and others, we detect a disposition to rely on a foreign body for support, their frustules being usually embedded in the mucus of some member of the family Palmellaceæ.” Recently I have had an opportunity of ascertaining that Epithemia gibba is strictly an adherent species, and that its supposed exceptional character in this respect has been based on insufficient observation.
The Cytology and Histochemistry of the Neurones of Periplaneta americana
Authors: ASHHURST DOREEN E.
Published: April 2021

The only cytoplasmic inclusions visible in the neurones by the light microscope are the lipochondria and mitochondria. It is suggested that the Golgi bodies, seen in preparations made by the Golgi techniques, are produced by the deposition of osmium or silver on the surface of the lipochondria.

The lipochondria consist of phospholipids and cerebrosides. There is also some lipid in the cytoplasm, together with carbohydrates, proteins, and RNA.
Extrusion of nuclear material during oogenesis in Blatta orientalis
Authors: GRESSON R.A. R. , THREADGOLD L. T.
Published: April 2021

That nucleolar material is extruded to the cytoplasm of the young oocyte of Blatta orientalis is confirmed by means of electron microscopy. The nucleolus and nucleolar extrusions are shown to contain RNA. In addition to the nucleolar extrusions, vesicle-like structures originate in the nuclear membrane and from there pass into the cytoplasm where they become indistinguishable from elements of the endoplasmic reticulum. When the nucleolar extrusions reach the cytoplasm they increase in size, come into close association with a few mitochondria, and migrate towards the periphery of the cell. It is concluded that the emission of material from the nucleolus and the passage of vesicles from the nuclear membrane to the cytoplasm are necessary prerequisites for the process of vitellogenesis.
The fine structure and biology of the egg-shell of the wheat bulb fly, Leptohylemyia coarctata
Authors: Hinton H. E.
Published: April 2021

The egg-shell of Leptohylemyia coarctata consists of 3 meshwork layers. The outermost wall is a sheet with perforations that are usually 5 to 10 μ wide. Across each of these perforations is a very fine network, the interstices of which are 0·1 to 0·2 μ wide. The middle meshwork layer is 2 to 7 μ thick. It is chiefly responsible for the mechanical strength of the shell. The inner meshwork layer is usually 2 to 4 μ thick. It consists of vertical columns extending inwards from the middle layer. The apices of the columns are branched in a plane normal to their long axes. These horizontal branches anastomose to form an open network, which is the innermost wall of the shell. The struts of all meshworks consist of fibrils 1 to 1·5 mμ · in diameter. The fibrils form a meshwork, the interstices of which are usually 2 to 5 m μ · wide.

When the egg is submerged in water, a film of air is held by the hydrofuge inner meshwork. This film of air functions as a plastron, but as a relatively inefficient one because above it there is a stationary layer of water 8 to 15 · thick held by the 2 upper meshwork layers, which are hydrophil. Between the shell and the subchoral cuticle there is a waxy membrane. This membrane is closely attached to the inner face of the shell. It plays an important part in the resistance of the egg to desiccation.
Studies on Campodea (Diplura) : the anatomy of the glands and sense-organs of the head
Authors: George Martin
Published: April 2021

Recent studies of the cephalic glands of Campodea have shown previous descriptions to be misleading in several respects. The campodeid salivary glands lie in the posterolateral parts of the head capsule and each is composed of a much-coiled ‘labyrinth’ and a distal end-sac. The histology of the two regions differs greatly, and although a little secretory activity has been observed in the end-sac, the labyrinth appears to be responsible for secreting most of the definitive saliva. The latter is passed to the outside down a median duct which opens between the ‘setigerous plates’ of the labium. Although the salivary glands of Campodea have homologues in other apterygote insects and the myriapods, the homology of the second pair of cephalic organs, the lobulate glands, is obscure. These glands, which are situated in the head and the anterior part of the prothorax, are composed of cells arranged around a system of ducts opening into the cephalic haemocoel. The ducts contain acidophil material which is secreted by the gland cells and numerous small cells which are perhaps haemocytes. The size of the lobulate glands relative to the size of the body increases as the animal matures, and it is possible that they are responsible for secreting some form of growth hormone. The cheek glands are situated beneath the epidermis of the lateral part of the head capsule and are composed of two different types of cells ; their homology and function are unknown. The paired lateral sense-organs also lie beneath the cephalic epidermis, but each is a bowl-shaped structure composed of numerous bifid sensory cells. The latter are innervated and each contains a bifid sensory rod. The distal prolongations of the sensory cells are interpolated between accessory cells whose cytoplasm contains granules. The latter may be either proximally or distally situated in the cell but are not composed of pigment. The definitive structure of these senseorgans is only attained in the sexually mature insect and they are only represented by disorganized groups of cells in the nymphs. Preliminary experiments are described which indicate that the lateral sense-organs are not concerned with the perception of optical stimuli and their function and similarities to other insect sense-organs are discussed.
Electron microscopy of the development of tracheoles in Drosophila melanogaster
Authors: Ahmad Shafiq S.
Published: April 2021

The tracheoblasts associated with the flight-muscles of Drosophila were studied by electron microscopy. During the developmental stages the cytoplasm of such tracheoblasts shows extensive membrane structures arranged in whorls. It seems that these membranes become aligned in pairs, spread out in tracheoblast cytoplasm, and form the walls of the new tracheolar vessels. The membranous whorls appear to have no obvious relationship with the usual endoplasmic reticulum, Golgi apparatus or plasma membranes. They are probably produced from certain large granules distributed irregularly in the cytoplasm of the young tracheoblasts.

Membranes limiting the tracheoles from the tracheoblast cytoplasm (the so-called mestracheons) are not usually seen in the younger stages. They are sometimes seen after the cuticular lining of the tracheoles has been formed.
The histology and histochemistry of development and resorption in the terminal oocytes of the desert locust, Schistocerca gregaria
Authors: Lusis O.
Published: April 2021

During vitellogenesis the follicular cells play an active part in the synthesis of yolk. The term ‘corpus luteum’ as applied to the ovary of the locust is invalid and two terms ‘white’ and ‘yellow* follicle have been introduced to describe the separate identities of the normal and pathological postovulatory follicle. The protein yolk is a protein- carbohydrate compound, presumably a glycoprotein. Three kinds of lipid bodies are present; the first is a phospholipid, the second a combined phospholipid and triglyceride, and the third triglyceride. Lipids are coloured by dissolved (β-carotene. Concentration or absorption of the lipids causes the crystallization of carotene and the formation of the pigment body. During resorption the follicular cells act as lecitholytic cells, first breaking down the protein and then the lipid yolk, and finally degenerating themselves. It is suggested that the oocytes have an inherent potential for resorption, the realization of which depends on various factors within the body.
Intranuclear lipids in the early oocytes of Heteropneustes fossilis (Teleostei)
Authors: Seshachar B. R. , Nayyar R. P.
Published: April 2021

Purely lipid bodies have been encountered inside the nucleus of early oocytes of Heteropneustes fossilis. These are mixtures of phospholipids and triglycerides. They occur independently of the nucleoli. With the growth of oocyte they increase in size and number and move towards the nuclear membrane. During later stages they diffuse out into the cytoplasm presumably to take part in yolk formation.
A general method for silvering invertebrate central nervous systems
Authors: Fraser Rowell C. H.
Published: April 2021

The best-known silvering methods are less successful with invertebrate than with vertebrate central nervous tissue. They fall into two classes with conflicting merits. In the first, metallic impregnation is assisted by accessory chemical agents, and subsequent development deposits only limited silver derived from the impregnating bath ; in the second, impregnation is in a simple silver nitrate solution, and the development is physical, the silver deriving from the developer. The most important part of the first process is impregnation, development adding relatively little; impregnation is comparatively slight in the second process, which relies much more on development.

If an impregnation of the first type is followed by physical development, the results have the advantages of both methods. The final picture is as good as that produced by the classic methods, and the reliability of the result greatly increased ; the method is successful with a variety of difficult invertebrate material. A method is described, using Blest’s modification of Holmes’s impregnator (class I) and Samuel’s physical developer (class II). The effects of temperature, pH, and duration of impregnation are described and related to the needs of different tissues. Increases in both temperature over the range 30° to 70° C and pH from 7·0 to 9·0 have similar and summating effects: increase in intensity of axon staining, increase in background staining, and decrease in fibre specificity.
Cytotaxonomy of ticks
Authors: Kahn J.
Published: April 2021

The material studied consisted of laboratory-bred specimens of 2 species of Prostriata and 8 species of Metastriata.

Ixodes ricinus and I. hexagonus (Prostriata) have XX : XY sex-determining mechanisms with diploid complements of 28 and 26 acrocentric chromosomes respectively. All the species of Metastriata studied have XX:XO sex-determining mechanisms with diploid complements of 21 and 22 chromosomes in males and females respectively. Haemaphysalis leporis palustris is the only species with metacentric chromosomes. Hyalomma spp., Dermacentor andersoni and Haemaphysalis leporis palustris each have X-chromosomes larger than any of the autosomes, whereas Rhipicephalus sanguineus and R. secundus do not have conspicuously large X-chromosomes.

In all the species studied early male meiotic prophase is characterized by a period of growth similar to that of oocytes at first meiotic division. This nuclear growth of the primary spermatocyte is thought to have evolved together with the production of a large-sized spermatozoon.

The structure of the testes and their accessory glands in Ixodes differs significantly from that of the corresponding organs in Metastriata. Ixodes also differs from the other genera studied as regards the splitting of the integument during ecdysis. It is suggested that Ixodes should be given the status of a ‘family’.
Adaptation of certain histological techniques for in situ demonstration of the neuro-endocrine system of insects and other animals
Authors: Dogra G. S. , Tandan B. K.
Published: April 2021

Three techniques for staining the secretory neurones in sections were applied directly to the whole brain and/or intact organs of the neuro-endocrine system of certain insects, and the whole brain of various invertebrates and vertebrates. After minor changes in the original procedures, in situ staining was achieved in those components of the neuro-endocrine system that are known to contain the neurosecretory material. With the Victoria blue staining technique, the secretory neurones, the neurosecretory pathway, and the storage-and-release organ were stained satisfactorily in all the experimental animals, in such a way that observations could be made in whole mounts or suitably dissected portions of the bulk-stained preparations. With the aldehyde-fuchsin and aldehyde-thionin staining techniques, the somata and the proximal portion of the axon of the neurones and the storage-and-release organ were usually stained satisfactorily enough for purposes of observation in the invertebrate material only. On sectioning the bulk-stained components of the neuroendocrine system and mounting the sections, the sites known to contain the neurosecretory material were revealed promptly. On comparing the information derived from mounts of the bulk-stained preparations with that derived from sections of similar preparations, and also with that derived from routine histological procedure, no difference was detected.
The fine structure produced in cells by primary fixatives 2. Potassium dichromate
Authors: Baker John R.
Published: April 2021

The exocrine cells of the mouse pancreas were fixed in potassium dichromate solution, embedded in araldite or other suitable medium, and examined by electron microscopy.

Almost every part of these cells is seriously distorted or destroyed by this fixative. The ergastoplasm is generally unrecognizable, the mitochondria and zymogen granules are seldom visible, and no sign of the plasma membrane, microvilli, or Golgi apparatus is seen. The contents of the nucleus are profoundly rearranged. It is seen to contain a large, dark, irregularly shaped, finely granular object; the evidence suggests that this consists of coagulated histone. The sole constituent of the cell that is well fixed is the inner nuclear membrane.

The destructive properties of potassium dichromate are much mitigated when it is mixed in suitable proportions with osmium tetroxide or formaldehyde.