bluuebunny/crossref_metadata_2025 huggingface dataset:
Micro-anatomical Studies on Asellus
Authors: Needham A. E.
Published: April 2021

The micro-anatomy of the autotomy mechanism in the thoracic appendages of Asellus is described; it shows considerable resemblance to that of Astacus, except in size. The fifth thoracic pair of appendages do not autotomize in the mature male Asellus. This depends on a very small anatomical difference, the closure of a fissure which is present in the exoskeleton of normally autotomizing limbs. The method of autotomy is inferred from observations, and from the arrangement of the muscles of the limb. The micro-anatomical changes which accompany the very rapid expansion of the oostegites in the female Asellus, are described. A system of ‘microtrichia’, probably homologous with that of insects, is described in Asellus and in certain other Crustacea. Its probable function is indicated. The pattern of pigmentation in Asellus is largely determined by the muscular system of the body, but is, nevertheless, probably adaptive. The pattern in other Isopoda is similarly determined but may be modified. Certain unrecorded differences between Asellus aquaticus and Asellus (Proasellus) meridianus are enumerated.
Cytochemical Differentiation between the Pentose and Desoxypentose Nucleic Acids in Tissue Sections
Authors: Sanders F. K.
Published: April 2021

Animal tissues contain two types of nucleic acid: the desoxypθntose, or thymo-, nucleic acids whose distributionis confined to the nucleus; and the pentose, or yeast, nucleic acids which can occur in both nucleus and cytoplasm. For many years.it has been possible to identify desoxypentose nucleic acid by means of the Feulgen reaction, although, as has been frequently pointed out (Lison, 1936; Stowell, 1943), this must be carried out under carefully standardized and controlled conditions if its results are to be reliable. No corresponding test for pentose nucleic acids existed until Brachet (1940, 1941) showed that it was possible to identify pentose nucleic acids by comparing sections stained with basic dyes with other sections similarly stained following treatment with a pancreatic extract containing the enzyme ribonuclease. Therefore a distinction between the two types of nucleic acid may be made by applying both the Feulgen and Brachet tests to the same material. However, since the stains used in the two cases are different, and one set of sections is subjected to acid hydrolysis and the other is not, it may be difficult to relate the two cytological appearances to one another.
The Effect of Removal of the Anterior Lower Sac on the Lateral Appendix in the Embryonic Olfactory Organ of Kaloula Borealis (Barbour)
Authors: Tsui Chi-Lan
Published: April 2021

The removal of the anterior lower sac from the embryonic olfactory organ of Kaloula borealis produced two different and opposite effects on the lateral appendix. In larvae 11-27 mm. in length the excision of the sac had a harmful effect and hastened the degeneration of the appendix. When the same operation was made on the larvae 28-38 mm. in length, however, the degeneration of the appendix was retarded. Early removal of the sac had also deleterious effect on the olfactory placode but did not, within the experimental period, influence its normal course of development.

Since the experimental animals made only limited growth in the laboratory, the later effects of the removal of the anterior lower sac remain unknown. It is planned to rear experimental larvae under more natural conditions.
A Simple Method for Cutting Sections in the 0·5 to 1 μ Range, and for Sections of Chitin
Authors: Wigglesworth V. B.
Published: April 2021

Tissues fixed and stained with osmium/ethyl gallate often require sectioning at 0·5 to 1 µ. In the method described they are double-embedded in agar and ‘ester wax’ (Steedman), cut on a film of water on the coverslip, and mounted in gum containing ethyl gallate. Prepared safety razor blades are recommended. This method is useful also for cutting serial sections of insect cuticle.
The Blood-cells of the Ascidian, Phallusia mammillata
Authors: Endean R.
Published: April 2021

The structure, histochemistry, and histogenesis of the blood-cells of Phallusia mammillata (Cuvier) have been investigated.

Primitive lymphocytes give rise, by a series of transition stages, to vanadocytes, pigment cells, phagocytes, and cells with acidic vacuoles. There is evidence that most of these cells must eventually leave the blood-stream. During the development of each cell type, RNA appears to be released from the nucleus, and there is a progressive reduction in nuclear volume.

Ninety-eight per cent of the total number of blood-cells are vanadocytes or their precursors. Each vanadocyte contains a number of globules. Each globule has a central core enclosed by a surface membrane containing compound lipid. In the core, a vanadium compound is associated with H2SO4, protein, and carbohydrate material, which may be the precursor of the tunicin of the test. Part of the carbohydrate material is in a dispersed form and can be hydrolysed with 2N H2SO4. The remainder is in the form of birefringent grains which resist hydrolysis, and appears to be a very insoluble polysaccharide.

Those lymphocytes that are destined to form vanadocytes develop vacuoles in their cytoplasm initially. In these vacuoles, which are ringed with granules that are probably mitochondria, granular material capable of reducing OsO4 and AgNO3 is formed. The vacuoles in each cell then unite to form one large vacuole, and refractile granules appear in the perinuclear cytoplasm. These granules then move out from the nucleus in the cytoplasm peripheral to the vacuole. Each refractile granule is then enclosed in a subspherical compartment in which protein material is formed. As the compartments are transformed into the globules of vanadocytes, acid, PAS-positive material, and a vanadium chromogen with reducing properties appear.

The pigment cells contain melanin and oriented submicroscopic crystallites.
p-toluenesulphonic acid as a fixative
Authors: Malm Mignon
Published: April 2021

p-toluenesulphonic acid in aqueous solution is introduced to histologists and recommended for fixation of the central nervous system by a three-step procedure: flushing the blood-vessels with a saline solution, filling the vessels with the fixative, and delaying the autopsy. With rats and guinea-pigs as test objects, a solution of at least 0·5 M gave excellent results, as evidenced by the minimum of cellular shrinkage, the absence of perivascular and perineuronal spaces, and the clarity of cellular membranes and basiphil material. The neurones, neuroglia, microglia, and blood-vessels were well defined when stained by conventional histological techniques. Cytological details became more prominent because the tissue had shrunk less than in routine preparations. The acid is non-volatile, colourless, pleasant to handle, and low in price.
The actions of enzymes on lampbrush chromosomes
Authors: Macgregor H. C. , Callan H. G.
Published: April 2021

The chromomeres of lampbrush chromosomes of Triturus cristatus are Feulgen-positive; they therefore contain DNA. After removal of their DNA in boiling trichloracetic acid, the chromomeres stain with fast green at alkaline pH; they therefore contain basic protein. The lateral loops are Feulgen-negative; they stain with toluidine blue at acid pH, but much less intensely following RNase digestion; they therefore contain RNA. The spheres of chromosomes V and VIII do not contain RNA.

Unfixed lampbrush chromosomes retain a life-like appearance in 0·07 M K/NaCl at pH 6·2; in this medium the nuclear sap disperses. As pH is raised to 8·5 the matrices of lateral loops dissolve but chromosome axes remain unbroken. Above pH 8·5 lampbrush chromosomes dissolve. As pH is lowered from 6·2, at between 5·8 and 5·4 coagulation occurs. If pH is rapidly reduced still further, a persistent relaxed condition sets in between 2·5 and 2.

In concentrations of K/NaCl above 0·5 M lampbrush chromosomes dissolve. Lateral loop matrices dissolve in 0·25 M K/NaCl but chromosome axes remain unbroken. In concentrations of K/NaCl below 0·05 M lateral loop matrices dissolve, but even in distilled water chromosome axes remain unbroken.

Trypsin at pH 6·2 and at pH 7·8 strips the matrices from lateral loops and occasionally breaks matrix fusions. It causes chromomeres to swell and coalesce, but fails to break chromosome axes. The action of ‘pan-protease’ resembles that of trypsin in all respects.

Pepsin at pH 6·2 strips the matrices from lateral loops, but does not destroy chromomeres. At low pH peptic digestion is slow: the enzyme is attacking coagulated chromosomes; but if peptic digestion precedes a lowering of pH the overall outcome is a rapid solution of loop matrix, and under these conditions matrix and sphere fusions are broken. If trypsin or ‘pan-protease’ digestion precedes a lowering of pH there is a similarly rapid solution of loop matrix; thus the action is not specifically referable to pepsin. Under no conditions does pepsin break the axes of lampbrush chromosomes.

RNase at pH 6·2 strips the matrices from lateral loops; this action is detectable at extreme dilution. RNase does not destroy chromomeres, nor does it break chromosome axes. If tryptic digestion follows RNase digestion this too fails to break chromosome axes.

Unlike the proteolytic enzymes and RNase, DNase at pH 6·2 breaks the fibril between adjacent chromomeres, and it also breaks the axes of lateral loops.

Contrary to Mazia’s experience with salivary gland chromosomes, versene does not break the axes of lampbrush chromosomes even when applied in media of low electrolyte concentration.

These results indicate that uninterrupted fibres of DNA run throughout the lengths of lampbrush chromosomes.

Contents
The structure and topography of stretch receptors in representatives of seven orders of insects
Authors: Osborne M. P. , Finlayson L. H.
Published: April 2021

In Ephemera (Ephemeroptera), Dictyopterygella and Isoperla (Plecoptera), Periplaneta and Blaberus (Dictyoptera), Forficula (Dermaptera), and Dytiscus (Coleoptera) there is a pair of stretch receptors on each side in the dorsal region of most abdominal segments. Each receptor consists of a connective-tissue strand to which is attached a single sensory neuron. One member of each pair is approximately longitudinal and the other approximately vertical in orientation.

In Sialis (Neuroptera-Megaloptera) the longitudinal receptor consists of a muscle-fibre and a neuron; the vertical receptor consists of a neuron with one or two long processes. Connective-tissue fibres are absent from both receptors.

In Limnophilus and Phryganea (Trichoptera) there is a longitudinal receptor only. It consists of a muscle-fibre to which is attached a tube of connective tissue containing the dendrites of the sensory neuron. The caddis receptor resembles closely the lepidopteran receptor.

No abdominal stretch receptors could be found in Rhodnius or Nepa (Hemiptera-Heteroptera), and in Schistocerca and Locusta (Orthoptera) no vertical receptors could be found.
The structure of the dragline control valves in the garden spider
Authors: Wilson R. S.
Published: April 2021

In the ducts of the major and minor ampullaceal glands of Araneus diadematus, special valves have been found which control the output of the dragline. Closure of the duct is achieved by inflation of the valve lips; opening is achieved by deflation. These valvular changes are brought about by groups of muscles attached to the duct.
Experiments on fixation for electron microscopy
Authors: Malhotra S. K.
Published: April 2021

The effect of fixation with acidified solutions of osmium tetroxide (pH 1·5 to 3·5 has been studied on the first (proximal) convoluted tubule cells of the kidney and the pancreatic exocrine cells of the mouse, by electron microscopy. Partially prepolymerized methacrylate was used for embedding. The various membranous structures and the ribosomes retain their individuality even after prolonged fixation in solutions containing 5% acetic acid (pH 1·5). However, the mitochondrial matrix and the ground cytoplasm are not preserved ; the zymogen granules are also partially washed out.
The unmasking of cytoplasmic lipids in rat livers as a consequence of dietary changes
Authors: Gahan P. B. , Bitensky L. , Chayen J. , Cunningham G. J. , Maggi V.
Published: April 2021

The livers from rats fed either on a normal diet containing 20% of protein or on a diet which facilitated liver carcinogenesis and which contained only 5 % of protein supplemented with methionine appeared histologically normal. Histochemical investigation of such livers showed that in the livers of animals fed on the protein-deficient diet there was a large increase in lipid staining. Biochemical investigation of these livers demonstrated that this increase in lipid staining was not due to a significant increase in total lipids nor to a significant decrease in total protein. These findings are discussed in terms of the ‘unmasking’ of the structural cytoplasmic lipids of the liver cells as the consequence of the feeding of an apparently protein-deficient diet.
Skeletal organization in the coral, Pocillopora damicornis
Authors: Wainwright Stephen A.
Published: April 2021

The skeleton of this Hawaiian reef coral was found to contain at least 99’9% by weight of the mineral aragonite, present as submicroscopic crystals in spheritic arrangements. The organic component of the skeleton comprises 0·01 to 0·1 % of the total weight and has 3 microscopic constituents: (1) filaments of lime-boring algae, (2) a dispersed network of fibres 1 μ in diameter, and (3) a transparent, milky, regionally biréfringent matrix of chitin. The chitin was observed to be a spongework of fibrils of average diameter 20 mμ. The chitin fibrils were inferred to be randomly oriented in the plane of the skeletogenic epithelium perpendicular to the direction of growth of the long axes of the aragonite crystals.

The development of the skeleton is traced from the initial mineral deposit by the larva after its attachment, through the formation of the larval skeleton and growth into the fully formed, branching colony. The process of formation of chitin fibrils according to the contour of the skeletogenic epithelium and the later deposition of aragonite crystals as described accounts for the formation of all skeletal elements of Pocillopora.

Evidence is presented for the hypotheses that (1) the amide group of the chitin molecule is responsible for the ability of certain organic substrates to be calcified (thus protein is not a necessary component of such substrates); (2) zooxanthellae in Pocillopora contribute a product of photosynthesis to the coral as the monomer of the chitin matrix; and (3) chitin synthesis thus depends on the activity of zooxanthellae and the rate of chitin synthesis controls the rate of skeletogenesis in Pocillopora.
A study of the replacement mechanism of the pulmonate radula
Authors: Runham N. W.
Published: April 2021

Results obtained from a histological, autoradiographic, and operative investigation of the radulae of two pulmonates have led to the formulation of the following theory of radula replacement. The radula is secreted continually by the permanent odontoblasts and continually moves anteriorly. The superior epithelium of the radular gland is produced by division of cells near the odontoblasts and moves forward at the same rate as the radula; the cells produce materials that harden the radula and then die. The inferior epithelium is also produced by division of cells near the odontoblasts, but initially moves anteriorly at only a quarter of the rate of the radula. The epithelium then changes shape from a columnar to a pavement epithelium. It is suggested that it then moves forward at the same rate as the radula. The pavement epithelium secretes the subradular membrane which may serve to attach the epithelium to the radula, and the supralateral radula tensor muscles are attached to the basement membrane of this epithelium. At the extreme anterior end of the radula the inferior epithelium becomes again columnar and secretes a cuticle continuous with the buccal cuticle. This process detaches the subradular membrane and the radula from the epithelium. The epithelial cells then die and disintegrate. The detached radula and subradular membrane show a change of staining properties suggestive of reversal of the tanning, and they then break up.
Haematopoietic nodules as centres of fat synthesis in the liver of the migratory starling, astor roseus
Authors: George J. C. , Naik D. V.
Published: April 2021

A histological and histochemical study of the haematopoietic nodule in the liver of Pastor roseus was made from October to April. The formation and development of the haematopoietic nodule by aggregation of lymphocytes and monocytes was found to be a continuous process, in which new nodules are formed regularly. The older nodules after a certain period of high activity show a considerable decline in the activity of blood-cell formation. The fully formed haematopoietic nodules give rise to different types of blood-cells—erythrocytes, granular leucocytes, lymphocytes, and monocytes. During the pre-migratory period the lymphocytes and monocytes were found to be more numerous in the nodules. It is likely that the number of erythrocytes increases during migration and that the formation of different types of blood-cells depends upon demand. It is concluded that fat is synthesized in the lymphocytes, monocytes, and free-moving reticulo-endothelial cells, but that this synthesis is mainly carried by the reticulo-endothelial cells. The phagocytes may also be the carriers of fat, and it is suggested that they are later modified into fat-cells in the fat-depot. Haematopoiesis in this bird is a normal phenomenon occurring in the liver in all seasons and is not a pathological condition.
The use of methyl green as a histochemical reagent
Authors: Baker John R. , Williams Elizabeth G. M.
Published: April 2021

The cation of methyl green carries two positive charges, that of malachite green only one; but the two dyes behave towards tissue-constituents in almost exactly the same way. These dyes are not specific for chromatin. They colour certain objects that are devoid of DNA, even when they are used in very dilute solution. The granules of cells called Körnchenzellen in the connective tissue of the common snail, Helix aspersa, are strongly coloured by both dyes from very dilute solutions, and thus provide a striking instance of the unspecificity of these dyes.

Malachite green, which is stable and free from contamination by metachromatic impurities, can advantageously replace the methyl green commonly used in mixtures with pyronine.

It is suggested that pyronine may have a greater capacity for penetrating into closetextured objects, such as nucleoli and ribosomes, than methyl and malachite greens.
The fine structure of the body-wall in a free-living nematode, Euchromadora vulgaris
Authors: Watson B. D.
Published: April 2021

The body-wall of adult Euchromadora vulgaris is composed of the 3 layers common to all nematodes, the cuticle, epidermis, and muscle cells. The cuticle is composed of 4 layers, a thin membrane resolvable only by the electron microscope, and 3 layers which can be observed in the light microscope. Histochemical tests show that the cuticle is predominantly protein and contains collagen. Of the 3 main layers of the cuticle, the outermost is about 0.4 μ thick and it is penetrated at regular intervals by grooves which divide the cuticle into annuli. This layer has several features in common with the external cortical layer of the cuticle in Ascaris lumbricoides; it is hardened by disulphide bonds and possibly quinone tanning, and is resistant to collagenase. The middle layer is about 1 to 1.3 μ thick and is formed from a series of overlapping plates. The rod-like bodies of de Man are located in this layer and are hollow. Internally, the cuticle is bounded by a basal lamella about 02 μ thick. The epidermis is thickened to form 4 chords and is composed of a large number of cells, which contain filamentous mitochondria with many cristae, granules of glycogen, and, in the pharyngeal region, pigment spots. The fibrillar zone of the muscle cell contains myofilaments of two types, large filaments 20 to 25 mμ in diameter, which are surrounded by smaller filaments 5 to 7 mμ in diameter. There are filamentous mitochondria, glycogen and a nucleus in the protoplasmic bulb. Covering the muscle cell is a thin membrane, the sarcolemma, which is infolded at regular intervals between groups of myofilaments. The sarcolemma is fused with the basal cuticular layer at both ends of each muscle cell.
The fine structure of RNA-storing archaeocytes from gemmules of fresh-water sponges
Authors: Ruthmann August
Published: April 2021

Gemmules of fresh-water sponges contain about 500 binucleated cells (‘archaeocytes’) which are loaded with reserve substances including ribonucleoprotein, acidophilic proteins, lipids, and polysaccharides. These substances are utilized during the early phase of histogenesis after germination of the gemmules. Apart from the presence of reserve bodies, the basic fine structure of metabolically inactive archaeocytes within the closed system of a gemmule is not fundamentally different from actively metabolizing cells of rapidly growing tissues. In particular, ribosomes, endoplasmic reticulum, mitochondria, Golgi bodies, and RNA-containing nucleoli are present during inactivity as well as after germination and resumption of growth and synthesis. Changes in cellular fine structure after germination include an increased density of the cytoplasmic ground substance, the appearance of small vesicles in the vicinity of the Golgi bodies and of annulate lamellae and a large, cylindrical centriole near the nuclear envelope. Two general conclusions are drawn from these results. Neither the ultra- structural aspect of a cell nor the presence of high concentrations of RNA in cytoplasm and nucleolus is a valid indication of cellular activity or inactivity. The persistence of Golgi bodies and endoplasmic reticulum through long periods of inactivity shows that their structural integrity is not dependent upon continuous energy input, although these intracellular membrane systems are undoubtedly dynamic structures in metabolically active cells.
Movement of palisade in locust retinula cells when illuminated
Authors: Horridge G. A. , Barnard P. B. T.
Published: April 2021

In dark-adapted eyes cisternae of the endoplasmic reticulum collect near the rhabdom and form around it a functionally significant region 2 to 4 μ across, of lowered refractive index. In light-adapted eyes this structure is dispersed as vacuoles in the cytoplasm, and instead mitochondria are crowded round the rhabdom. Onion bodies up to 8 μ. in diameter occur in the retinula cell cytoplasm.
An enzyme histochemical and electron microscopical study of the light organ of the glow-worm, Lampyris noctiluca
Authors: BARBER V. C. , PILCHER C. W. T.
Published: April 2021

The light organs of female specimens of the glow-worm Lampyris noctiluca were investigated by enzyme histochemical tests, lipid stains, and electron microscopy. Differences, both histochemical and in fine structure, were found between the cells of the photocyte and reflector layers. The photocytes contained a vesiculated reticulum, photocyte granules, amorphous granules, and numerous mitochondria. The reflecten layer did not contain the reticulum or the two types of granules and there were fewer mitochondria. Glycogen granules, and spaces possibly caused by the removal of urate during preparatory procedures, were present in this layer but absent from the photocytes.

All the dehydrogenase enzymes, except for glucose-6-phosphate, 6 phosphogluconic, lactic, and β-hydroxybutyric dehydrogenases, which were absent from both layers, showed more activity in the photocyte layer. NADH2 and NADPH2 diaphorase showed no activity in the reflector layer.

A transition zone between the two layers was demonstrated both histochemically and morphologically.

Alkaline and acid phosphatase could not be demonstrated in the light organ. The adenosine triphosphatase demonstrable in the organ was not activated by magnesium but was activated by calcium ions. Lipid was present in both layers of the organ.

The tracheolar supply to the photocytes was good but no tracheolar end organs were observed.

The dehydrogenase activity of the body musculature is also reported upon.
The pericardial cells of Drosophila melanogaster
Authors: MILLS R. P. , KING R. C.
Published: April 2021

The ultrastructure of the pericardial cells of adult female Drosophila melanogaster is illustrated. The data presented suggest that the pericardial cell internalizes by pinocytosis complex and possibly toxic compounds present in suspension in the haemolymph. These compounds are broken down to soluble molecules within lysosome-like vacuoles. The pericardial cells thus behave like the reticulo-endothelial cells of mammals.
A further note on the measurement of the affinity of a dye (Azure A) for histological substrates
Authors: Goldstein D. J.
Published: April 2021

If two histological sections, of thickness np. and znp, and having the same apparent intensity of staining, are at equilibrium with dyebaths of concentration B1 and B2 respectively, the affinity of the histological substrate for the dye is, under defined conditions, given by the expression ΔF° = −RT In I/B, where B is either (i) B2 if the thinner section is stained to saturation, or (ii) B1 if B1 = 3B2. The affinity tends to be greater when measured in a weaker dyebath, as implied in method (ii).

Evidence is presented suggesting that the uptake of the basic dye Azure A by pancreatic basal chromidial substance, goblet cell mucin and intestinal epithelial cytoplasm follows a Langmuir adsorption isotherm to a first approximation, in that, at low dyebath concentrations, the uptake of dye is proportional to the concentration of dyebath with which the substrate is in equilibrium, while in strong dyebaths the uptake approaches a plateau. A deviation from the ideal Langmuir isotherm in dyebaths of moderate concentration, observed in epithelial cytoplasm and to a lesser extent in pancreatic basal chromidial substance, may have been due to interaction between neighbouring dye-binding sites, or to the presence in a single area of sites with different affinities for the dye.
Note on the Cytological Localization of Alkaline Phosphatase
Authors: Lorch Joan
Published: April 2021

In comparing various techniques for the microchemical demonstration of alkaline phosphatase it was observed that with the method of Menten, Junge, and Green (1944) nuclear phosphatase cannot be demonstrated in epithelial cells, whereas with the Gomori-Takamatsu (1939) technique both nuclear and cytoplasmic elements (e.g. brush borders and the Golgi zone) of suitable organs show the presence of the enzyme. The substrate in the method of Menten, Junge, and Green is Ca α- or β-naphthylphosphate in the presence of α-naphthyl-diazonium hydroxide. In the Gomori technique the substrate is sodium-β-glycerophosphate. The failure of nuclear phosphatase to be demonstrated by the first method might be caused by:
Tests by Tissue Culture Methods on the Nature of Immunity to Transplanted Skin
Authors: Medawar P. B.
Published: April 2021

The transplantation of skin from one rabbit to another elicits a reaction that conforms in main outline with that of an actively acquired immunity. The experiments described in this paper were designed to test the hypothesis that the regression of such grafts is secured by the action of antibodies demonstrable in vitro.

Skin from adult rabbits has therefore been cultivated in the presence of serum and growing mesenchymal tissues derived solely from rabbits heavily and specifically immunized against it.

Immune sera and tissues are without effect on the survival, cell-division frequency and migratory activities of explanted skin, and agglutinins for epidermal cell suspensions are not demonstrable in immune sera.

With certain stated qualifications, it has therefore been concluded that the occurrence of free antibodies is not a sufficient explanation of the regression of skin homografts in vivo.
Some Observations on Mouse Spermatids
Authors: Bell L. G. E.
Published: April 2021

Mammalian spermatogenesis has recently been reviewed by Gresson (1951). He emphasized that there is no general agreement as to the nature of the mitochondrial sheath of the middle-piece. The points at issue seem to be whether it is spiral in structure and whether it is granular or a continuous band. Gresson (1950) claimed the sheath is a spiral, workers with the electron microscope (Randall and Friedlaender, 1950; Bretschneider and van Iterson, 1947; Bretschneider, 1949) claimed a spiral structure. This work has been done mainly on mature sperms. Gatenby and Woodger (1921) and Gatenby and Beams (1935) did not support the spiral structure, but gave evidence for the existence of separate granules in the spermatid middle-piece. Benda quoted in Wilson (1925) gave figures showing a granular and spiral structure, though the figures are not clear. While the present paper was being prepared, Austin and Sapsford (1952) published phase-contrast photomicrographs of surviving rat spermatids, and said that the mitochondria form a spiral structure developing from a granular to a continuous spiral. At the present time attention is centred on the cytochemical structure and physiological function of the middle-piece (Rothschild and Cleland, 1952). As a preliminary to cytochemical work, it seemed important to demonstrate the morphology in a convincing way, by using carefully chosen techniques of fixation especially suitable for cytochemistry (Bell, 1952; Gersh, 1952).
Formalin-Sensitive Cells in Spinal Ganglia
Authors: Bacsich P. , Wyburn G. M.
Published: April 2021

Spinal ganglia of rabbits and cats were prepared for histological examination in a variety of ways. Dark staining multangular cells are present in sections after fixation with formaldehyde succeeded by (a) alcoholic dehydration; (b) sectioning with the freezing microtome. Sections treated in other ways, including freezing-drying, only have the typical small and large round cells. It is suggested that certain groups of cells, sensitized by formaldehyde fixation, can react by shrinkage on subsequent treatment by alcoholic dehydration or other procedures.

FROM time to time it has been contested that there are different nerve cell types in the spinal ganglia and that, while the typical pseudounipolar cell dominates the cell population, it does not altogether monopolize it. Amongst the first to study the cells of spinal ganglia were Retzius (1894), Dogiel (1896), Lenhossék (1896), Ramón y Cajal (1906), Marinesco (1906), Nageotte (1907), and Marinesco and Minea (1908). Using different histological methods, they all commented on the occasional finding of nerve cells resembling motor cells. Kiss (1932) recorded the presence of a significant number of dark-staining ‘multipolar’ cells in the ganglia of spinal and cranial nerves after formalin fixation and prolonged treatment with osmium tetroxide. On the basis of their appearance, he suggested that they were visceral efferent cells. Blair, Bacsich, and Davies (1935) confirmed the presence of these characteristic cells in spinal ganglia fixed in formalin. They could, however, find no evidence of multiple cell processes. They therefore preferred to describe them as ‘multangular’ rather than multipolar cells, and concluded that any assessment of function would depend on experimental evidence.

The present work is an account of the effect of various methods of fixation, including freezing-drying, on the cytology of spinal ganglia, with special reference to alterations in shape and staining reaction.
The Mechanism of Cell-division A Study with Carbon Monoxide on the Sea-Urchin Egg
Authors: Swann M. M.
Published: April 2021

1. Developing eggs of the sea-urchin Psammechinus miliaris were subjected to carbon monoxide inhibition, which was controlled by changing from green to white light. The behaviour of the eggs was recorded by time-lapse photography.

2. If inhibition is applied before the eggs enter mitosis, their first cleavage is delayed by a time which is roughly equal to the period of the inhibition.

3. If the inhibition is applied when the cells have already entered mitosis, they complete mitosis and cleave with little or no delay, but their second cleavage is delayed by a time which is roughly equal to the period of the inhibition.

4. It is suggested that the necessary energy for the second mitosis and cleavage is being stored up during the first mitosis and cleavage, and that this energy store operates like a reservoir which is continually being filled but siphons out when it is full. Once the energy has siphoned out, it carries mitosis and cleavage through, even though the reservoir is not filling up because of carbon monoxide inhibition.
Surface Forces in the Tracheal System of Insects
Authors: Wigglesworth V. B.
Published: April 2021

The mechanism by which the tracheal system becomes filled with air is reviewed. It is concluded that the fluid contents are actively absorbed by the walls of the system. The air often enters from the atmosphere through the spiracles. In some insects the system fills while the insect is submerged in water or while the spiracles are closed. It is shown by means of simple models how the tanning of the lining of the larger tracheae or the secretion of wax over the walls will bring about the liberation of gas from solution when the fluid is subjected to a very slight negative pressure.

The movements of fluid in the tracheole endings of insects are also reviewed. The removal of fluid which takes place during activity, particularly under conditions of deficient oxygen supply, is not caused by secretory activity but by the physical forces produced by the products of metabolism.

The evidence supports the view that the fluid in the tracheoles is a cell sap whose passage up the tracheole under the action of capillarity is opposed by the elasticity or swelling pressure of the cytoplasmic sheath of the tracheoles. It is shown by means of a simple gelatin model how osmotic changes in the surrounding fluid, acting by way of a cytoplasmic sheath, will bring about the absorption of such a cell sap.

A more exact model, illustrating the greater permeability of the inner wall of the tracheole which the proposed mechanism requires, is provided by the anal papillae of mosquito larvae. These structures show the same adaptation to a saline medium as is postulated in the tracheoles of mosquito larvae from salt water.

Alternative mechanisms are discussed. It is suggested that the capillary forces in the tracheoles are probably small. The effects of probable contamination of the tracheole fluid by an oily film (Beament) and the effects of changes in hydrogen-ion concentration on interfacial tensions are illustrated by reference to further models.
The Atrial Nervous System of Amphioxus (Branchiostoma)
Authors: Holmes William
Published: April 2021

This paper is concerned with the system of neurons which lies in the walls of the atrium of Branchiostoma.

The system is found on the parietal and ventral walls of the atrium, as well as round the gut, and it is therefore thought preferable to speak of it as the atrial nervous system rather than the autonomic (enteric) system (Boeke).

The neurons are shown to lie in or immediately below the atrial epithelium, which is of ectodermal origin.

Special attention is given to the innervation of the gut and its diverticulum, of the atrio-coelomic funnels, and of the atrioporal region.

Evidence as to the effector and receptor elements of the system is discussed. It has central connexions, and it is suggested that its activities play an important part in the animal’s behaviour.
Undulatory Propulsion
Authors: Gray J.
Published: April 2021

1. Typical undulatory progression over a rigid environment depends on three fundamental factors:

(i) Internal bending couples change the lateral curvature of each region of the body to that previously characteristic of the region lying immediately anterior to itself.

(ii) The phase of lateral bending varies along the length of the animal’s body.

(iii) The presence of external restraints prevents all regions of the body from moving along any path other than one tangential to their own circumference of curvature.

2. The magnitude of the forward tangential thrust imparted to the body depends on (a) the magnitude of the internally generated bending couples, and (b) the form of the waves. If friction operates on the surfaces of external restraint the thrust also depends on the coefficient of lateral friction and on the position of the restraints.

3. From a mechanical point of view, an undulating organism (irrespective of its size and internal structure) can be regarded either as a series of curved levers or as a series of inclined planes.

4. The general principles of undulatory swimming are the same as for a terrestrial glide, except for the fact that each element of the body must possess a component of motion normal to its surface if it is to contribute towards the propulsion of the animal; this type of motion can only occur when the waves move backwards relative to the ground. The animal cannot move forward as fast as the waves are propagated over the body.

5. The propulsive powers of three-dimensional waves are limited to the extent to which the organism is restrained by external forces from spinning about its own longitudinal axis. Otherwise the principles of progression are the same as for twodimensional waves: the resultant of all the forces acting normally to the body is equal but opposite to that of all tangential forces.
The Effect of Phenylthiourea on Pigmentation by Melanin in the Developing Frog, Eleutherodactylus martinicensis
Authors: Millott Norman , Lynn W. Gardner
Published: April 2021

The black pigment cells in the skin, iris, and retina of Eleutherodactylus martini-censis (Tschudi) are melanophores. Under the influence of 0·01 percent, phenylthiourea the melanin disappears in about 84 hours at laboratory temperatures. After administration of the substance for 5 days, discontinuance of treatment is followed by return of the pigment within 72 hours, to an extent at least equal to that normally attained in untreated controls. The stages of disappearance and reappearance of this pigment have been studied in the gross embryo, skin, iris, and retina, as well as in individual melanophores.
Observations on the Nerve Fibres of Aurellia aurita
Authors: Horridge Adrian
Published: April 2021

The nerve fibres of Aurellia aurita were originally described by E. A. Shafer from gold preparations. This work has been repeated with Holmes’s method of silver staining on the slide. Results have beert obtained substantially in agreement with those of Shafer.

The same nerves can be seen in the living animal when a phase-contrast microscope or oblique illumination is used. By the use of these techniques, a study has been made of the plan of the nerve net over the subumbrellar surface of the bell.

This work is intended as an anatomical foundation for physiological studies to be described elsewhere.
Spicule Form in Leucosolenia complicata
Authors: Jones Walter Clifford
Published: April 2021

The tri- and quadriradiates of Leucosolenia complicata are described in four aspects: surface view, transverse view, side view, and planar view. The spicule form and size vary with the distance from the oscular edge in all four cases.

In planar view (when the eye is directed along the optic axis) the spicule rays usually appear straight and thus exhibit a tendency to grow in planes which intersect in a line having the direction of the optic axis. The angle between the oscular ray planes (the planar angle) is always greater than 120° and the spicules hence belong to the ‘secondary sagittal’ class of von Ebner. The planar angle is not closely correlated with the optic angle and varies from about 160° at the oscular edge to about 140° at the base of the tube. This variation precludes the possibility that the angle is simply controlled by the crystallizing properties of calcite.

The curvature of the choanoderm is a factor controlling spicule form because the formative calcoblasts move in contact with this layer when secreting their respective rays.

Reasons are given for returning!,, coriacea (Montagu) to a separate genus, Clathrina.
The Mechanism of Proboscis Movement in Arenicola
Authors: Wells G. P.
Published: April 2021

The mechanism of proboscis movement is analysed in detail in Arenicola marina L. and A. ecaudata Johnston, and discussed in relation to the properties of the hydrostatic skeleton.

Proboscis activity is based on the following cycle of movements in both species.

Stage I. The circular muscles of the body-wall and buccal mass contract; the head narrows and lengthens.

Stage IIa. The circular muscles of the mouth and buccal mass relax; the gular membrane (or ‘first diaphragm’ of previous authors) contracts; the mouth opens and the buccal mass emerges.

Stage IIb. The longitudinal muscles of the buccal mass and body-wall contract; the head shortens and widens and the pharynx emerges.

Stage III. As Stage I.

The two species differ anatomically and in their hydrostatic relationships. In ecaudata, the forward movement of body-fluid which extrudes and distends the proboscis is largely due to the contraction of the gular membrane and septal pouches. In marina, the essential mechanism is the relaxation of the oral region which allows the general coelomic pressure to extrude the proboscis. The gular membrane of marina contracts as that of ecaudata does, but its anatomy is different and it appears to be a degenerating structure as far as proboscis extrusion is concerned.

Withdrawal of the proboscis may occur while the head is still shortening and widening in Stage 116, or while it is lengthening and narrowing in Stage III. The proboscis is used both in feeding and in burrowing; in the latter case nothing enters through the mouth; the difference is largely caused by variation in the timing of withdrawal relative to the 3-stage cycle.
Experiments on the Mechanism of Silver Staining: III. Quantitative Studies
Authors: Peters A.
Published: April 2021

The quantitative aspects of silver staining of sections have been investigated with radioactive silver (Ag111). The concentrations of reducible silver, developed silver, and silver nuclei in the sections were determined, but it is doubtful if the values obtained for silver nuclei are significant.

All three forms of silver increased with pH, time, and the concentration of silver in the impregnating solution. Temperature of impregnation had little effect on the uptake of reducible silver, but increased the developed silver, presumably by increasing the silver nuclei. An increase in the temperature of a hydroquinone-sulphite developer increased the amount of reducible silver reduced by the developer. The deposition of silver by a glycine physical developer was shown to follow a curve which was reasonably consistent with the assumption of a typical autocatalytic reaction.

The uptake of silver by non-nervous tissues provided evidence that the process is not specific for nerves; the final specificity of staining is determined during development.

The quantitative results are consistent with the hypothesis that the histidine in the sections is responsible for the combination of reducible silver.
Experiments on the Mechanism of Silver Staining: IV. Electron Microscope Studies
Authors: Peters A.
Published: April 2021

Silver-stained sections of nervous tissue were examined with an electron microscope. It has been shown that the developed silver is particulate. These particles are between 30–700 Å in diameter and in nerve-fibres they are disposed along the surface and inside the components of the fibre. When impregnated sections were developed in a glycine physical developer, the mean size of the developed silver particles increased with an increase in the time of development.

In silver-stained sections of human sympathetic ganglion, the silver particles were distributed throughout the cell, but were more densely aggregated in the cell membrane and the nucleus. Erythrocytes show a dense aggregation of silver particles throughout the cytoplasm.
Studies of the impregnation of nervous tissue elements: I. Impregnation of axons and myelin
Authors: Wolman M.
Published: April 2021

All metallic impregnation methods depend on the presence of reducing groups in tissues. By testing the effect of various reduction indicators on sections of nervous tissue it was found that some reduction systems do not have a high enough oxidizing potential to serve for the visualization of either axons or myelin. Others can visualize myelin sheaths. The systems having the highest potential visualize also axons. Although myelin can be oxidized more easily than axons, axons are probably relatively richer in reducing groups.

Impregnation by AgNO3 or Ag-diammine results in the formation of silver nuclei in both axons and myelin. Subsequent exposure of such sections to the action of reducing agents increases the visible impregnation of the axons much more than that of the myelin. This effect can be ascribed to the low dielectric constant of myelin.

Gold toning serves a dual purpose: (a) coating with gold the more heavily impregnated structures, and (b) clearing the background through the displacement of the silver from the less intensely impregnated areas.

The mechanism of metallic impregnations and the rationale of the different steps in Bielschowsky’s procedure for axons are discussed.