bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development of the Otoliths of the Mouse
Authors: Lyon Mary F.
Published: April 2021

The development of the otoliths in mice from days’ gestation to 3 days after birth was studied in alcohol-, formalin-, and Bouin-fixed material. The first sign of the otoliths in alcohol-fixed day material was an apparent protein precipitate. Then a PAS-reacting substance appeared among the protein, together with biréfringent particles. Calcium salts were then deposited in their typical crystalline form and the otolith flattened so that at days it consisted of a gelatinous layer surmounted by a layer of biréfringent calcareous granules with an organic matrix, which contained polysaccharide and phosphatase. Glycogen was also present. After formalin fixation very little otolith material was seen until days, and with Bouin very little until 2 days after birth; formalin preserved the calcium salts and granular matrix, Bouin the granular matrix only. Comparison of the results of the various fixatives showed that the localization seen after alcohol fixation was unreliable, so that the position of the otolithic material when it first appeared, and hence the site of its secretion, were unknown. The cells of the maculae showed phosphatase activity and probably took part in secreting substances; the secretory regions of the utriculus may also have done so. The mechanism of concentration and precipitation of the calcium salts remains unknown, but it is suggested that the polysaccharide matrix may take part.
The Developmental Origin of Hereditary Absence of Otoliths in Mice
Authors: Lyon Mary F.
Published: April 2021

Hereditary absence of otoliths occurs in some mice homozygous for the mutant pallid. The development of the ears of pallid mice, with and without otoliths, was compared with that of normal mice. In ears lacking otoliths all parts of the developing otoliths could be detected, except the calcium salts. Abnormality was first detected at days’ gestation, when the normal birefringence due to calcium salts did not appear; from days some ears of pallid mice showed a normal layer of calcium granules while others lacked it. The gelatinous layer of the otolith matrix appeared at the normal time, and was normal in amount, position, and staining reactions. The granular matrix was not clearly present at the earliest stages, and days, at which it is normally seen. From days, however, abnormal ears contained free debris which, from its staining reactions, was interpreted as granular matrix. This debris was found in the sacculus and later the endolym-phatic sac. At and days’ gestation ears lacking otoliths showed hydrops of the cochlear duct, sacculus, and endolymphatic duct. Possible mechanisms for the failure of calcification and for the hydrops are discussed. All ears of pallid mice lacked pigment from the secretory regions. The ears of six other mouse mutants, some affecting pigment, and others affecting hearing and behaviour but not pigment, were examined for pigmenta-tion. The pigment of the ear paralleled that of the eyes, and there was no correla-tion between lack of ear pigment and presence of behaviour defects.
The Effect of Prior Intravenous Injections of Dissociated Epidermal Cells and Blood on the Survival of Skin Homografts in Rabbits
Authors: Billingham R. E. , Sparrow E. M.
Published: April 2021

A study has been made of the effect of prior intravenous injections of living homologous dissociated epidermal cells and blood-cells on the survival of skin homografts subsequently transplanted from the cell donors in rabbits. These treatments failed to elicit an immune response resulting in the accelerated breakdown of the skin homografts, even when a massive dosage of homologous blood was administered. On the contrary, in a high proportion of animals injected with their intended donors’ epidermal cells it was found that the host’s capacity to react against the skin homografts was abrogated to an extent that actually increased their survival by a factor of 2 or 3. This prolongation of survival is not merely the outcome of the non-specific treatment of a host with epidermal cells as such, since pre-treatment of animals with suspensions of their own epidermal cells was ineffective in prolonging the survival of homografts. This modification in the host’s response was not obtained by the administration of epidermal cell suspensions by other routes; when the cells were injected intradermally a state of immunity was elicited, and their intraperitoneal injection was without demonstrable effect. The injection of living cells was found to be obligatory since cells killed by freezing and thawing before their injection had no effect on the course of the homograft reaction. The injection of homologous blood gave results comparable with those obtained with epidermal cell suspensions, although they were not as consistent. Evidence is presented suggesting that a state of immunity towards grafts of homologous skin may be evoked by prior intradermal injections of epidermal cell washings not containing intact living cells. Possible explanations and affinities of the induced abrogation of a host’s immunological response to skin homografts are discussed, as well as its possible implications.
The Development of the Neural Tube of the Chick Embryo. A Study with the Ultraviolet Microscope
Authors: Hughes Arthur
Published: April 2021

The development of the spinal cord and dorsal root ganglia of the chick has been studied by ultraviolet photomicrography of sections at 2,537 Å. The results have been compared with material treated by standard neurohistological methods. In the ultraviolet negatives cytoplasmic density for unit thickness of section has been measured for ependymal and ventral horn cells, and also in the neuro-blasts of the dorsal root ganglia. The density of the mitotic figures in the ependymal layer has also been measured. The changes in cytoplasmic density in developing neurones closely parallel those in the RNA concentration of the whole embryo. In the developing neurone a high density of RNA is seen within the cyto-plasm for some days after the cell has first differentiated. This then falls and later rises slowly once again as Nissl substance is laid down. Experiments on the effect of ribonuclease on ependymal mitotic figures and the cytoplasm of neuroblasts are described.
A New Technique for the Cultivation of the Chick Embryo in vitro
Authors: New D. A. T.
Published: April 2021

A new technique is described for the cultivation of chick embryos in vitro. It consists essentially in supporting the explanted blastoderm on a piece of vitel-line membrane stretched across a glass ring. The nutrient medium is fluid albumen. Primitive streak blastoderms explanted by this technique: (a) frequently develop as far as the formation of a functional blood circulation, together with flexion and torsion of the embryo; (b) show normal expansion across the vitelline membrane; (c) develop at a normal rate until after the 20-somite stage.
Mitotic cell death and delay of mitotic activity in guinea-pig embryos following brief maternal hyperthermia
Authors: Edwards M. J. , Mulley R. , Ring Shiela , Wanner R. A.
Published: April 2021

Pregnant guinea-pigs were exposed to an environmental temperature of 42·0–42·5 °C for 1 h on day 21 of gestation. Their embryos were removed at periods from 45 min of heating to 48 h following exposure. Histological preparations of embryos showed clumping of nuclear chromatin and subsequent death of cells which were at about the stage of mitosis. Affected cells were particularly numerous in the central nervous system. Further mitotic activity was inhibited for 6–8 h. Squash preparations of the telencephalon at 1 h after heating showed an increase from 3 to 86 % in the number of mitotic cells showing damage in the form of nuclear clumping; this number fell progressively to 30% by 24 h after heating. The proportion of cells in various stages of mitosis changed considerably at 1–8 h after heating, but had returned to pre-heating values by 24 h. The proportion of cells in prophase fell markedly, while the proportion of metaphase cells was doubled at 4 h after heating, indicating blocks to the cell generation cycle before prophase and in metaphase.
Analyse expérimentale de la régulation du nombre des cellules germinales après déficience gonadique chez le poulet
Authors: Didier Par Eliane , Fargeix Noël , Bergeaud Yves
Published: April 2021

Experimental study of the regulation of the number of germ cells following gonadial deficiency in the chick

Colonization of the genital ridges by germ cells was quantitatively studied in control chick embryos killed at stages 25–29, and in embryos in which a surgical excision of the gonad presumptive area was made previously on the second day.

In operated embryos which show a more or less perfect agenesis of one gonad, the number of germ cells counted in genital ridges is lower than the number of germ cells estimated in the same stages of control embryos. The deficit is greater for left gonadic agenesis. The decrease in the total number of germ cells is essentially due to a reduction in the cells colonizing the deficient gonad. There is no excess of germ cells observed in the control gonad.

Accordingly, a right side operation strengthens the asymmetry of germ cells distribution, whereas a left side one reduces it.

Thus, in birds the regulation of the number of germ cells and the quantitative control of colonisation of the gonads is at the gonad level.
The neural cell cycle in the looptail (Lp) mutant mouse
Authors: Wilson Doris B. , Center E. M.
Published: April 2021

The cell cycle of mesencephalic ventricular cells was studied by means of tritiated thymidine radioautography during normal and abnormal development in the looptail (Lp) mutant mouse. The total generation time, DNA-synthetic (S), premitotic (G2), mitotic (M), and postmitotic (G1) periods were compared in looptail homozygotes (Lp/Lp) which exhibit neural dysraphism and in their normal littermates ( + / + ) at 10 and 11 days’ gestation. Both normal and abnormal embryos showed a chronological lengthening of the generation time between the 10th and 11th day. However, the generation time in the 10-day abnormal brains was 4·5 h longer than that in normal littermates, and the difference was the result of an increase mainly in the M and G1 periods. At 11 days of gestation the generation time in the abnormal brains increased by 5·0 h over that of the normal brains. Since the cell cycle was actually prolonged in the defective brains, the increased numbers of mitotic figures which characterize the looptail homozygote brain during early development appear to reflect the lengthening of the mitotic period rather than increased proliferation.
Fine structural study of cell migration in the early mesoderm of normal and mutant mouse embryos (T-locus:t9/t9)
Authors: Spiegelman Martha , Bennett Dorothea
Published: April 2021

Mouse embryos homozygous for the t9-allele exhibit an enlarged primitive streak, scanty mesoderm, and aberrant axial organization by the eighth day of development and die by the tenth day.

Light and electron microscopic observations of sections through mesodermal cells of these mutant embryos reveal sheet-like arrangements of cells rather than the array of stellate individual cells seen in mesoderm of normal embryos. The abnormal mesodermal cells usually display lobate pseudopodia instead of the filiform pseudopodia typical of normal mesodermal cells. These lobopodia do not possess the subsurface microfilaments characteristic of filopodia. Cellular junctions such as those regularly seen between adjacent filpopodia of normal mesodermal cells occur only very rarely between neighboring lobopodia of mutant mesodermal cells.

The deficiency of mesoderm may be due to the failure of cells to form the cellular associations typical of gastrulation and to move normally from the primitive streak which consequently becomes enlarged due to the accumulation of apparently immobilized cells. Those few cells which do attain the proper location nevertheless do not appear well-differentiated. Their abnormalities of cell shape, cellular translocation, and cellular interactions may be related to a lack of microfilament cytostructure and surface adhesiveness.
Studies on effects of 5-bromodeoxyuridine on the development of explanted early chick embryos
Authors: Lee H. , Deshpande A. K. , Kalmus G. W.
Published: April 2021

Chick embryos were explanted at stages ranging from the definitive streak to one-somite and cultured for 19–21 h on thin albumen with or without 5-bromodeoxyuridine (BrdU) (2–12 μg/ml). BrdU primarily inhibited neurulation which was found to be stage dependent. If exposed to BrdU at the definitive streak stage, it resulted in an open brain region; if treatment was delayed until the head-process stage, it inhibited the closure of the midbrain and, to some extent, the hindbrain, but the forebrain closure was mostly unaffected. BrdU had no appreciable effect on later stages. It was also found that BrdU inevitably inhibited somite formation when exposed to 8 μg/ml or higher concentrations. The blastodermal expansion, heart development, and blood island formation were usually not affected.

Cytological changes were observed in adversely affected tissues, particularly the neural tissue. BrdU produced nuclear enlargement and clumped metaphase, but did not cause extensive necrosis.

The grafting experiments showed that an increase in the concentration of BrdU from 4 to 12 μg/ml progressively inhibited the self-differentiation of Hensen’s node grafts. However, BrdU (8 μg/ml) had no significant effect on the inducing capacity of node grafts nor the competence of the epiblast.

Autoradiographic studies showed that the application of BrdU, at 6 μg/ml or lower, caused no obvious variations in the incorporation of [3H]uridine into chick embryonic cells. BrdU, at .10—12 μg/ml, selectively inhibited the uptake of [3H]uridine in the neural tissue.
The effect of 5-bromodeoxyuridine on early mouse embryosin vitro
Authors: Garner Wendy
Published: April 2021

The effect of 5-bromodeoxyuridine (BudR) on the development of cleavage stage mouse embryos has been examined. The analogue was found to have a deleterious effect at relatively low doses on survival to blastocyst, and to a lesser extent on trophoblast outgrowth in supple- mented medium. No tendency to suppress differentiation rather than cell division was detected. Possible mechanisms for the BudR effect are discussed.
Microfilaments in the external surface layer of the early amphibian embryo
Authors: Perry Margaret M.
Published: April 2021

A comparison was made by transmission electron microscopy of the microfilaments in the surface layers of the early embryos of Triturus alpestris and Xenopus laevis at stages of development up to neurulation. Actin-like filaments which bound heavy meromyosin (HMM) were found in cell extracts of all stages, but were comparatively rare in the newly fertilized egg. Ten nm microfilaments were present throughout development in Xenopus, and from the mid-neurula stage in Triturus. Both kinds of microfilament were located in the circumferences of superficial ectoderm cells at the level of the apical junctions, the .10 nm microfilaments in association with desmosomes which began to develop before gastrulation in Xenopus. The accumulations of microfilaments in the apical constrictions, which form in ectoderm cells of Triturus early gastrulae when dissociated in a calcium-free medium, suggest that they are contractile elements. In the absence of such accumulations in the cell apices, the reverse curling exhibited by Xenopus ectodermal explants is attributed rather to a separation of the cells’ lateral borders. Cytochalasin B (5 μg/ml) caused ectodermal explants from the early gastrulae of both species to disaggregate. With the rupture of the apical junctions there was a disorganization of the associated microfilamentous layer.
The determination of polarity in the developing insect retina
Authors: Lawrence P. A. , Shelton P. M. J.
Published: April 2021

The retina in Oncopeltus fasciatus is a polarized structure in which all ommatidia are orientated the same way. By a series of grafting experiments we have shown that the orientation of ommatidia is partly dependent upon the orientation of the epidermis from which they develop and partly on the orientation of the host eye. Grafts which invert the dorsoventral axis of the presumptive eye epidermis do not disrupt the orientation of the nascent ommatidia. Grafts which are rotated by 90° or 180° produce altered patterns of orientation. The polarity of the epidermis is to some extent conserved in these cases. Significantly ommatidia at the graft/host border take up orientations intermediate between the extremes found in the graft and host. Small rotated grafts assume the polarity of the host retina. These results are compared with the effects of similar grafts on developing insect bristle patterns.
The development of the retinotectal projection inXenopuswith one compound eye
Authors: Feldman Joan D. , Gaze R. M.
Published: April 2021

Double-nasal and double-temporal compound eyes were constructed in Xenopus embryos at stages 32 and 37/38. A particular half was removed from the host eye anlage and replaced with the opposite half-eye from the contralateral side of a donor embryo. Control operations consisted of removing a half-eye and replacing it with a similar half from the ipsilateral side of the donor embryo. Whereas in control animals, each half-eye projected its fibres to the appropriate half-tectum, in operated animals each half of the compound eye spread its optic terminals across the entire rostrocaudal extent of the dorsal tectal surface.

The area of tectal surface covered by ganglion fibre terminals was similar in operated animals mapped at successive stages of development to that previously observed in normal animals at equivalent stages. Therefore the factors responsible for the extended distribution of fibre terminals from each half of a compound eye must exist at least from mid-tadpole life, and thereafter be continuously present throughout development.
A photographic study of development in the living embryo of Drosophila melanogaster
Authors: Bownes Mary
Published: April 2021

The changes which can be seen occurring during the development of a living embryo of Drosophila melanogaster are described in detail, and represented photographically as a series of developmental stages. This provides an easy, but accurate technique for selecting eggs at precise developmental stages for experiments.
Restoration of the capacity to form pole cells in u.v.-irradiatedDrosophilaembryos
Authors: Warn Richard
Published: April 2021

Injection of pole plasm into u.v.-irradiated posterior poles of early Drosophila embryos leads to the restoration of the capacity to form pole cells in nearly half of the recipients. The effect is specific, since cytoplasm from the anterior tip has no such result. In most cases only a small number (between 1 and 5) of discrete pole cells are formed. However, a large number of pole cell fragments with or without nuclei occur. Occasionally pole cells were formed outside the area of the originally irradiated pole plasm. This happened when material was injected more anteriorly than usual. Thus polar cytoplasm contains some factor(s) necessary for the formation of pole cells.
The matrix of the optic vesicle-presumptive lens interface during induction of the lens in the chicken embryo
Authors: Hendrix Richard W. , Zwaan Johan
Published: April 2021

The cell coats of the presumptive lens cells and the extracellular interface between the lens rudiment and optic vesicle were investigated in the chicken embryo throughout the period during which lens induction is presumed to take place.

Histochemical methods showed that the cell coats contained both glycoproteins and glycos-aminoglycans. Autoradiography after [3H]glucosamine injection indicated incorporation of the precursor with subsequent localization primarily at the cell surface. No obvious changes in the properties of the coat were noted with the progression of early lens morphogenesis.

The extracellular matrix at the interface between ectoderm and optic vesicle also contained glycoprotein and glycosaminoglycan. There was a heavy concentration of [3H]glucosamine-containing macromolecules in the area. Electron microscopy revealed that the interface consisted of the basement membrane systems of lens and optic vesicle, fused with their external fibrillar layers. In contrast to the findings on cell coats, the density of the interfacial matrix increases appreciably during the lens induction period. Evidence suggests that the cells of the two ocular epithelia are themselves the source of the matrix materials.

It is proposed that the macromolecules excreted by the epithelial cells into the interface interact at different concentrations to form aggregates of various structure by a process of self-assembly. This may be reflected in the different ultrastructure of the layers of the inter-facial matrix.

Quantitative changes in the density of the matrix, leading to increased adhesion between lens rudiment and optic vesicle, may restrict the lateral spreading of the lens cells and so fix the basal area of the lens rudiment. This, together with continued cell replication, may produce the cell crowding, placode formation and invagination characteristic of lens morphogenesis.
Nicotinamide adenine dinucleotide levels in chick limb mesodermal cells in vitro: effects of 3-acetylpyridine and nicotinamide
Authors: Rosenberg Martin J. , Caplan Arnold I.
Published: April 2021

The studies reported here show that in cultures of developing mesodermal cells, chondrogenic expression is associated with a progressive decline in cellular NAD+ levels. Furthermore, reduced cellular NAD+ levels resulting from exposure to the nicotinamide analog 3-acetyl-pyridine are correlated with a 2- to 100-fold potentiation of chondrogenic expression. Conversely, elevated NAD+ levels resulting from exposure to nicotinamide alone are correlated with inhibition of chondrogenic expression. These data are consistent with the hypothesis that pyridine nucleotides, or some derivative thereof, play a central role in the control of muscle and cartilage development in embryonic chick limbs.
The development of embryos in the uteri of mice treated with actinomycin D before implantation
Authors: Finn C. A. , Bredl J. C. S.
Published: April 2021

This investigation follows the development of embryos in the uteri of mice in which the differentiation of the implantation chamber has been retarded by the administration of actinomycin D before implantation.

For the first 48 h after the induction of implantation both embryonic and extra-embryonic parts of the blastocyst develop, but after 72 h the embryonic parts cease to grow and die. The giant cells and other extra-embryonic tissues, on the other hand, continue to develop for a much longer period, up to 288 h.

It is suggested that the actinomycin D, by delaying the formation of the implantation chamber in the endometrium, interferes with the formation of a proper functional connection between the trophoblast and endometrium with the result that the embryo receives insufficient nutrition for its development.
Immunochemical analysis of water-soluble antigens of chick retina in the course of embryogenesis
Authors: Mikhailov A. T. , Barabanov V. M.
Published: April 2021

Water-soluble antigens of chick retina were investigated using rabbit antisera to total extract and to individual electrophoretic fractions of retinal extract by methods of immunoelectrophoresis and Ouchterlony precipitation test. In the retina of the adult chick six serum and eleven tissue antigens were demonstrated. The tissue antigens of the retina comprised one organ-specific antigen and ten inter-organ antigens which were characterized by nonuniform distribution in tissues and organs of adult chick. Three antigens out of these were found only in tissues of the eye (retina, iris) and in the brain - inter-organ antigens of ‘narrow’ specificity. The other seven inter-organ antigens were found in tissues of brain and eye, as well as in various tissues and organs of hens - inter-organ antigens of ‘broad’ specificity.

A high degree of antigen similarity between retina and iris was observed. Anti-retina sera in chick lens could detect only inter-organ antigens of ‘broad’ specificity.

In the course of embryogenesis the first to appear in the developing retina were interorgan antigens of ‘broad’ specificity (on 3rd day of incubation). Formation of antigens of this group was completed by the 9th day of incubation. On the contrary, inter-organ antigens of ‘narrow’ specificity appeared later, in the period of histogenesis of retina (from 5 to 18 days of incubation). The organ-specific antigen of retina was found by 7th day of incubation.

One of the inter-organ retinal antigens of ‘narrow’ specificity (retina-iris-brain) appeared in the developing chick brain at the same time as in retina - on 10th—11 th day of incubation. Using the indirect immunofluorescence antibody technique this antigen was identified in the cytoplasm of retinal cells and brain neurones, but was not detected in the nerve fibres.
Cell proliferation in the developing wing-bud of normal andtalpid3 mutant chick embryos
Authors: Ede D. A. , Flint O. P. , Teague P.
Published: April 2021

Previous measurements on mitotic division rate or cell cycle time have been made on samples from a few discrete limb regions or by continuous sampling, but only down a unidimensional limb axis, disregarding morphological discontinuities such as the presence or absence of cartilage. This study presents a new analysis on normal and talpid3 mutant chick embryos, measuring mitotic rate and also cell density through the central proximo-distal axis and at the limb periphery, taking into account the development of cartilage regions. Differentiation of cartilage is correlated with a marked drop in mitotic rate, accounting for a proximo-distal gradient of mitosis in central counts which was not observed at the limb periphery. Talpid3 limbs at an early stage show a central mitotic gradient, but the reverse of that observed in normal limbs.
The early development of haploid and aneuploid parthenogenetic embryos
Authors: Kaufman Matthew H. , Sachs Leo
Published: April 2021

The early development of parthenogenetically activated oocytes has been studied in. C57BL × CBA-T6T6 (F1T6) translocation heterozygote mice and C57BL × CBA-LAC (F1LAC) mice. All F1T6 oocytes had either a quadrivalent or a univalent-trivalent configuration at meiosis I; no such chromosome configurations were observed in the F1LAC oocytes. At ovulation 36·5% of the F1T6 oocytes had 19 or 21 chromosomes, whereas 97% of the F1LAC had the normal haploid chromosome number of 20. After parthenogenetic activation, chromosome counts at metaphase of the first cleavage mitosis were made of the eggs with a single pronucleus following extrusion of the second polar body. These activated eggs had similar frequencies of 19, 20 and 21 chromosomes as had the oocytes at ovulation. The activated 1-cell eggs were transferred to the oviducts of pseudopregnant recipients and the embryos recovered 3 days later. At this stage of development, most of the F1T6 embryos with 19 chromosomes were no longer found, but the frequency of 21-chromosome embryos was similar to the frequency of 21-chromosome oocytes and activated eggs. There was a similar mean number of cells in the embryos with 20 and 21 chromosomes.

The results indicate that nearly all the embryos with 19 chromosomes failed to develop, probably beyond the 2-cell stage, whereas oocytes with 21 chromosomes had a similar development to oocytes with 20 chromosomes up to the morula stage.
Mitotic activity of germ cells during normal development ofXenopus laevistadpoles
Authors: Ijiri Ken-Ichi , Egami Nobuo
Published: April 2021

Data on the spatio-temporal pattern of germ cell proliferation in Xenopus laevis tadpoles were obtained, tracing the germ cells from the cloacal position forward. This spatial pattern in germ cell distribution and its change during normal development clearly coincided with histological observations of germ gland development. By application of regression lines to the analysis of this complex pattern, an interesting conclusion about the mitotic activity of germ cells was suggested. While the mitotic activity of germ cells before sexual differentiation shows a regional difference along the germ-cell-containing ridge (GCCR), the doubling time of sexually differentiated gonia seems to show a uniform value over the whole GCCR.
Abnormalities in the differentiation and cellular properties of hyperplastic lens epithelium from strains of chickens selected for high growth rate
Authors: Clayton R. M. , Eguchi G. , Truman D. E. S. , Perry M. M. , Jacob J. , Flint O. P.
Published: April 2021

Similar morphological abnormalities of the lens of the eye of two unrelated strains of chicks, both of which had been selected for high growth rate, were found to be associated with epithelial cells showing marked deviations from the normal in cell surface properties, mitotic rate, capacity for differentiation, and in DNA, RNA and protein metabolism. The relationship between these modified properties and the observed morphology is discussed.
Complete preimplantation development in culture of parthenogenetic mouse embryos
Authors: Kaufman Matthew H. , Sachs Leo
Published: April 2021

The present experiments were undertaken to determine whether, in parthenogenesis, heterozygous embryos develop better than homozygous embryos. Such experiments may provide an approach to elucidating whether fertilized embryos develop better than parthenogenetic ones because of heterozygosity, or if the sperm provides another contribution necessary for complete embryonic development. The parthenogenetic embryos studied included uniform haploids after extrusion of the second polar body, mosaic haploids in which each blastomere contained a genetically different haploid nucleus, and heterozygous diploid mouse embryos. Eggs were activated and cultured in a chemically defined medium. About three times as many mosaic haploid or heterozygous diploid eggs developed beyond the 4-cell stage after 98-100 h and to the blastocyst stage after 120 h in culture, than uniform haploid eggs. This indicates that the development of parthenogenetic embryos is probably under genetic control and that there was a better development of the heterozygous embryos. Mosaic haploid embryos showed the same high frequency of development as heterozygous diploids. The results therefore indicate that heterozygosity provided a developmental advantage even when distributed between two genetically different clones of cells in the same embryo.
Effects of formamide on neuroepithelial cells and on interkinetic nuclear migration in the chick embryo
Authors: Messier Paul-Emil
Published: April 2021

Young chick embryos were incubated on media containing formamide at concentrations of 0·1,0·25, 0·31,0·37, 0·43 and 0·5 M. Tn the neuroepithelium of these embryos we found that (1) the 0·1 M concentration had no detectable effect, (2) the 0-25 M concentration only affected mitosis which was blocked in metaphase so that mitotic figures accumulated near the neuro-coele, (3) 0·31 M formamide totally inhibited interkinetic nuclear migration and affected only slightly the cell asymmetry, (4) the 0·37 M concentration considerably reduced the amount of cytoplasmic microtubules and that the cells became round, (5) at 0·43 M formamide, all microtubules had disappeared and all cells were spherical, (6) at 0·5 M formamide all cells were spherical, detached from one another and the epithelium had lost its usual characteristics. Our results on exposure of the cells to low temperature (2 °C) suggest that formamide directly affects microtubules. All the effects observed at concentrations up to 0·43 M formamide are reversible.
A descriptive study of the rate of elongation and differentiation of the skeleton of the developing chick wing
Authors: Summerbell Dennis
Published: April 2021

Differentiation of the wing skeleton is clearly visible in whole mounts from stage 24. It proceeds in proximo-distal and postero-anterior sequence. It is possible to map the part of the limb giving rise to each skeletal element as it appears and subsequently. This enables one to estimate: (a) a rate of elongation curve for each segmental level, (b) the intrinsic rate of change of elongation of the cartilage, (c) a definitive extrapolation back to classical presumptive fate maps, (d) the normal range of variation in the proportion of the limb occupied by the three main segmental levels (stylopod, autopod, zeugopod).
Etude de la mise en place de la patte imaginale deTenebrio molitor: 1. Analyse expérimentale des processus de restauration au cours de la morphogenése
Authors: Huet CL. , Lenoir-Rousseaux J. J.
Published: April 2021

Adult leg development of Tenebrio molitor: IExperimental analysis of the restoration process during morphogenesis

The leg of the last instar larva, and especially the pharate pupa, of Tenebrio molitor (Colebptera) shows considerable restoration ability. Restoration refers to the regeneration of leg structures removed during the last larval instar. This process involves only those tissues adjacent to the cut surface. At each level of the leg, amputation before a characteristic time leads to the restoration of a complete leg, but thereafter the new segments formed are hypomorphic or just lobes. After an amputation close to the pupal ecdysis, fragments are obtained, and these incomplete structures show that the restoration process has ceased. Just before the pupal ecdysis the leg is withdrawn from the cuticle, so a very late amputation does not effect the leg tissue and a complete pupal and adult leg is formed.

The whole of the larval leg participates in adult leg morphogenesis, and histological techniques demonstrate a great correspondence between larval and adult leg segments. The larval trochanter, however, forms the adult trochanter and the proximal part of the femur. The larval tibia forms the adult tibia plus tarsus, except for the adult claws which develop from the larval tarsal claw.
Cell specific events occurring during development
Authors: Rutherford Charles L.
Published: April 2021

Ultra-microfluorometric techniques were adapted to follow the time sequence of glycogen degradation during the differentiation of two cell types in Dictyostelium discoideum. Glycogen content, glycogen phosphorylase activity, and inorganic phosphate accumulation were localized in specific cell types during stalk and spore development.

Glycogen levels in pre-stalk cells remained constant during the pseudoplasmodium and early culmination stages of development. However, as pre-stalk cells migrated into the position of stalk formation, a cell specific degradation of glycogen was observed. The loss of glycogen from pre-stalk cells was accompanied by an increase in the activity of glycogen phosphorylase. This increase in activity from 0·04 to 0·14 moles/h/kg dry wt. occurred as pre-stalk cells entered the position of stalk formation. An inverse relationship was found between glycogen levels and inorganic phosphate (Pi) levels in the developing stalk. During the process of stalk construction, a gradient of Pi levels occurred from the apex to the base of the developing stalk. Glycogen degradation from pre-spore cells lagged behind that of pre-stalk cells. No change in pre-spore cell glycogen levels was observed until stalk construction was nearly completed. The results emphasize the importance of the physical position of a cell with respect to its composition and fate during development.
Isoenzyme transitions of creatine phosphokinase, aldolase and phosphoglycerate mutase in differentiating mouse cells
Authors: Adamson Eileen D.
Published: April 2021

Extracts of embryonic mouse tissues (skeletal, cardiac and smooth muscle, and brain) were analysed by Cellogel electrophoresis, for their isoenzymic distributions of three enzymes, creatine phosphokinase, aldolase and phosphoglycerate mutase. Embryonic tissues from the 12th day to the end of gestation were examined for isoenzyme transitions, and it was found that the adult forms of these enzymes appeared during gestation. Extracts from cloned teratocarcinoma cells were similarly examined in order to determine their degree of bio-chemical differentiation. Undifferentiated embryonal carcinoma cells contained only the early embryonic forms of all three enzymes, while differentiated cells formed in vivo, and in some cases in vitro, started to express the adult types of creatine phosphokinase and aldolase. Thus, biochemical parallels have been demonstrated between developing embryonic tissues and teratocarcinoma cells differentiating in vitro.
Cell death in ovarian chambers ofDrosophila melanogaster
Authors: Giorgi F. , Deri P.
Published: April 2021

An ultrastructural analysis has been made of certain ovarian chambers undergoing abnormal development. The earliest morphological change in these chambers consists of the alteration of the nuclear material which is then followed by engulfment of portions of the nurse cell cytoplasm, including the nuclear fragments, into the overlying follicle cells. The continuation of this process leads to the progressive disappearance of nurse cells with the concomitant formation of huge dense vacuoles in the follicle layer. The morphological features described in the present investigation are similar to those found in other tissues and interpreted as leading to cell death. It is suggested that certain ovarian chambers undergo cell death as a result of the incapability of fürthering their development. The role played by cell death in oogenesis is also discussed on the basis of the current literature.
Evolution of the nucleolar apparatus during oogenesis in Acipenseridae
Authors: Raikova E. V.
Published: April 2021

Evolution of the nucleoli has been followed during oogenesis in the Acipenserid fishes, Acipenser ruthenus (the sterlet) and A. güldenstädti (the sturgeon) using light and electron microscopes. In the ovaries of adults, the oogonial nuclei usually have a single nucleolus with an adjacent mass of paranucleolar fibrillar material. The cytoplasm of the oogonia contains two dense bodies peculiar only to gonocytes, one being electron dense and containing RNA and the other being electron-lucent and lacking RNA. Neither is surrounded by membrane. The fine structure of the electron-lucent body is identical to that of the paranucleolar material, while the RNA-containing body structurally resembles the nucleolus. A nuclear origin for both cytoplasmic bodies is likely.

Leptotene-stage oocytes usually still have a single nucleolus. During zygotene, it is adjacent to the nuclear envelope and opposite to the chromosomes contracted in synizesis. At pachytene, a ‘cap’ of extrachromosomal chromatin is formed under the nuclear envelope and around the nucleolus. Bivalents also contact this cap. In early diplotene, the primary nucleolus still persists. The material of the cap is dispersed beneath the entire nuclear envelope in the form of granules of extra DNA; each granule then produces a peripheral (secondary) nucleolus. These become typical amphinucleoli with differentially developed granular parts, depending on the age of the nucleolus and the stage of meiosis. Their fibrillar parts always face the nuclear envelope. New peripheral nucleoli continue to form as long as granules of extra DNA persist under the nuclear envelope, i.e. approximately until vitellogenesis.

In early vitellogenesis, the peripheral nucleoli become transformed, by re-distribution of their fine structural components, into circular threads trailing towards the centre of the nucleus. The axis of the thread consists of fibres and is coated with granules. In late vitellogenesis, the nucleoli round up and become vacuolized; they are then peripheral again.

Proteinaceous RNA-lacking structures which are also produced in the nuclei during oogenesis in the Acipenseridae, are the ‘nuclear bodies’ and. ‘spheres’. The former are adjacent to peripheral nucleoli, the latter form on lampbrush chromosomes. Both are ultra-structurally alike. The loops of lampbrush chromosomes produce also RNP bodies (‘granules’ of Callan & Lloyd, 1960) which are ultrastructurally similar to nucleoli but lack segregation of granules from fibres into spatially distinct parts.

The evolution of the nucleolar apparatus during oogenesis in the Acipenseridae closely resembles that in amphibians.
Mechanisms of teratogenesis*
Authors: Saxén Lauri
Published: April 2021

In view of the great number of teratogenic factors known and the vast array of congenital defects, disorders and syndromes, it would probably be a waste of time to search for unifying mechanisms and principles in abnormal development. Instead, therefore, I shall describe a selection of teratogens and their consequences, and try to arrange them in a certain hierarchy based on a simplified model of how they act.
Cleft palate induction in hamster fetuses by glucocorticoid hormones and their synthetic analogues
Authors: Shah Ravindra M. , Kilistoff Alan
Published: April 2021

The effect of prenatal administration of different doses of cortisone, corticosterone, dexamethasone, triamcinolone and prednisolone on the fetus and its palatal development was studied. All the glucocorticoids, except cortisone, produced cleft palate in the fetuses. Both the total frequency and morphologically different types of cleft palate were related to the dose of the teratogen. Triamcinolone appeared to be more potent than other glucocorticoid in inducing cleft palate. An association was noted between fetal growth inhibition, the dose of the teratogen and the frequency and type of cleft palate.
Cell division patterns in the Drosophila head disc : clones on the head cuticle
Authors: Ransom Robert
Published: April 2021

An account of the patterns of clones induced on the head cuticle of Drosophila melanogaster is given. The system was studied using mitotic recombination, induced by X-rays at certain developmental stages. In agreement with the findings of a computer model devised to simulate growth in the head imaginal disc, cuticle clones are found to have a characteristic pattern, sweeping round the central, eye-forming part of the disc. The similarity between model and experiment suggests the validity of the model assumption. It is also shown that cuticle clones are not smaller in the posterior of the head, when induced at the developmental stages studied : this is in contrast to clones in the compound eye, where posterior clones are smaller than anterior ones.
Effects of testosterone implants in pregnant ewes on their female offspring
Authors: Clarke I. J. , Scaramuzzi R. J. , Short R. V.
Published: April 2021

Pregnant ewes were implanted with 1 g testosterone between days 30 –80, 50 –100, 70 –120 or 90 –140 of gestation. Ewes treated between days 30 –80 and 50-100 showed increased aggressive behaviour and clitoral enlargement, whereas this was not seen in the day 70 –120 or 90 –140 groups. Although the implants released similar amounts of testosterone at all stages of gestation, plasma testosterone concentrations were lower in the day 70 –120 and 90 –140 groups. The increased testosterone clearance in late gestation could be a result of increased placental aromatization. Masculinization of the genital tubercle was complete in female lambs in the day 30 –80 group, partial in the day 50 –100 and 70-120 groups, and absent in the day 90-140 group. These results therefore suggest that the ‘critical period’ for masculinization of the external genitalia is between days 40 and 50 of foetal life. In contrast to this anatomical masculinization, one aspect of behavioural masculinization had a later critical period, since female lambs of 30 –80, 50 –100 and 70 –120 day groups adopted male-like urination postures, whereas the day 90 –140 offspring showed the normal female pattern.
Biochemical and cytochemical studies on adenylate cyclase activity in the developing rat submandibular gland: differentiation of the acinar secretory compartment
Authors: Cutler Leslie S. , Rodan Sevgi B.
Published: April 2021

To investigate membrane changes in development of the exocrine cells of the rat submandibular gland (SMG), biochemical and cytochemical studies of adenylate cyclase activity were performed on prenatal and postnatal glands. SMG rudiments and glands were studied from 15 days of gestation up to birth and 1, 2, 3, 4 and 24 weeks after birth. Glands were chemically assayed for adenylate cyclase activity using the procedures of Salomon and coworkers and cytochemically studied using a procedure which was verified biochemically. At .15-16 days of gestation basal adenylate cyclase activity was low and no staining could be observed. Adenylate cyclase activity rose six-fold from the 16th to the 18th day of gestation. Adenylate cyclase staining became evident along the surface of most of the cells of the rudiment at this time. Basal adenylate cyclase activity remained relatively constant from the 18th day of gestation up to 24 weeks of age. However, sequential changes were seen in the cytochemical localization, especially in relation to the apical plasma membrane of the developing secretory cells.
The permeability to cytochalasin B of the new unpigmented surface in the first cleavage furrow of the newt’s egg
Authors: Selman G. G. , Jacob J. , Perry M. M.
Published: April 2021

Two to 10 μg/ml cytochalasin B (CB) caused retraction of the first cleavage furrow in Triturus eggs, a spreading of the unpigmented surface from the furrow region and a flattening of the whole egg. CB appears to act against the contractility of the microfilamentous band at mid-cleavage so as to relax the furrow and also to weaken unpigmented surface to allow the egg to flatten. Uncleaved eggs and the initial formation of the cleavage groove were unaffected by CB. A fully-retracted first cleavage furrow reformed itself on transfer of the egg to normal medium but only at the time of second cleavage. Initiation of second cleavage depended upon there being sufficient of the original pigmented surface on the animal hemisphere.

Tritium-labelled CB of high specific activity was prepared and used to study its ability to penetrate the surface of newt eggs during cleavage. Scintillation counting of whole eggs showed that CB was not taken into the newt egg until mid-cleavage (about 17 min after the double stripe stage) when new surface began to spread in the cleavage furrow. Fixation in glutaraldehyde and osmium tetroxide retained radioactivity in the egg, but more CB was retained after fixation in osmium tetroxide alone than after double fixation. Most of the retained radioactivity was in yolk platelets. Autoradiographs were prepared of sectioned eggs which had been fixed at late cleavage after [3H]CB had flattened the furrow. These showed that CB entered the egg through the unpigmented surface which formed in the furrow but it could not enter through the pigmented surface. The impermeability of the pigmented surface explains the observations that CB does not prevent initial furrowing at cleavage. Once inside the egg CB is transported slowly. CB penetrates to a limited extent beneath the pigmented surface from its border with the unpigmented surface in the first cleavage furrow and this seems insufficient in some circumstances to suppress the contractile phase of second cleavage.