bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of meiotic germ cells in the gonads of foetal mouse chimaeras
Authors: Mclaren Anne , Chandley Ann C. , Kofman-Alfaro Susana
Published: April 2021

The gonads of 53 foetuses (16♀, 37♂) derived from fusion of embryos at about the 8-cell stage were examined. Ovotestes were found in two of the male foetuses. When gonads were sectioned days post coitum, germ cells in meiotic prophase were seen in 6/6 female and 4/14 male foetuses. When air-dried preparations were made from gonads days post coitum, germ cells in meiotic prophase were seen in 7/7 females and 4/13 males. At days post coitum, 2/2 female but only 2/10 male foetuses showed any meiotic cells, and these were degenerating.

[3H]Thymidine injected into the mother days post coitum resulted in labelling of the meiotic germ cells, but the sex vesicle characteristic of meiotic cells in normal males was never seen. The timing of DNA synthesis and meiosis was identical to that seen in the germ cells in foetal ovaries.

We conclude that the meiotic cells seen in the testes of foetal chimaeras are probably XX in constitution, and rarely survive beyond the 19th day of gestation.
Effect of yolk-sac antibody on rat embryos grown in culture
Authors: New D. A. T. , Brent R. L.
Published: April 2021

It has been shown that congenital malformations can be produced in rats by injection into the pregnant female of rat kidney antiserum (Brent, Averich & Drapiewski, 1961 ; Brent, 1966a, b) or heterologous placental antiserum (Brent, 1966a, b, 1967). The teratogenic factor has been localized in the gammaglobulin fraction of the serum (Brent, 1966b).
Localisation et durée des potentialités médullo-surrénaliennes des crêtes neurales chez l’ embryon de Poulet
Authors: Chevallier Alain
Published: April 2021

The localization and duration of the capacity of neural crest cells to differentiate into medullary cells of the adrenal gland

The capacity of the neural crest cells to differentiate into medullary cells of the adrenal gland has been tested for different levels of the cephalo-caudal axis of the chick embryo and at different stages.

The procedure consisted in associating a fragment of neural crest cells containing spinal cord with a section of an embryo containing the prospective cortical territory. The latter was previously deprived in ovo of presumptive medullar adrenal cells by localized X-irradiation of its spinal cord.

The portion of the spinal cord which has the capacity to give off medulloblasts is located not only within the prospective adrenal area (somite levels 18–22), but also within a region extending over a length of six somites in front and seven somites behind the presumptive zone.

This capacity, which is restricted in space, is also limited in time. It is possessed by the portion of spinal cord defined above from 6 h before the migration of the first neural crest cells and lasts roughly for 24 h after the beginning of migration. Furthermore, the experiments indicate that the differentiation of neural crest cells into medullocytes requires the inductive influence of the cortical
Evolution de Fiode, 127I, total thyroïdien chez l’embryon de Poulet au cours de l’ incubation
Authors: Daugèras Nicole , Lachiver François
Published: April 2021

Thyroid, iodine in the developing chick embryo

Total thyroidal 127I of chick embryo has been studied from the 7th to the 20th days of incubation. On the 7th and 8th days the thyroid concentrates 127I but this concentration is weak. The total amount of 127I, Q, increases from the 8th day (0.1 ng) to the end of incubation, where its value is nearly 4·6µg. Between the 12th and 13th days there is an abrupt rise of the daily increment, ΔQ = Q2–Q1, and of the rate of accumulation, ΔQ/Q1. Between the 17th and 18th days there is a decrease of the increment and the rate of accumulation.
Evolution of the lining bodies in the embryonic chick gonad
Authors: Rahil Kuldeep S. , Narbaitz Roberto
Published: April 2021

Gonads from White Leghorn chick embryo of various ages ranging from 4 to 10 days of incubation, were fixed in half-strength Karnovsky’s fixative, osmicated and embedded in Araldite. Thin sections were stained with uranyl acetate and lead citrate. Our observations were especially concentrated on the germinal epithelium.

Two cytological characteristics not previously described in embryonic chick gonads were observed:A network of fine microfilaments was present in the somatic cells of the germinal epithelium. These microfilaments were especially concentrated in the apical pole of these cells and appeared to be more numerous in 5- and 6-day gonads. Since similar microfilaments have been described in other embryonic epithelia in which growth of glands or cords is taking place, their presence in the embryonic gonad may be related to the formation of sex cords.Lining bodies, organelles which are characteristic of follicular cells in the adult ovary, were found in the embryonic gonads of both sexes. They first appeared in some of the 5-day embryos and were present thereafter in all 6-day left gonads, in all left ovaries and in those left testes in which regression of the germinal epithelium had not been completed. Lining bodies were never observed in right germinal epithelia. It is classically accepted that follicular cells of the adult originate from the somatic cells of the germinal epithelium. The presence of lining bodies in the epithelial cells of young embryos appears to indicate that, despite the fact that follicles are not formed until after hatching, follicular cells initiate their differentiation much earlier. The fact that this differentiation is also present in gonads of male embryos can be interpreted in the light of current theories on sex differentiation which assume the bisexuality of embryonic gonads.Short cytoplasmic processes, representatives of a merocrine secretory process, have been described by other authors in the germinal epithelium of young embryos. We confirmed these observations and found, in addition, that these processes were smaller, both in size and number, in the right gonads. This fact, together with the previously mentioned absence of lining bodies in right gonads, appears to be the expression, at the ultrastructural level, of the well known asymmetry of the avian embryonic gonads.
The morphologic expression of each cardiac primordium in the chick embryo
Authors: Nadal-Ginard Bernardo , García María Paz
Published: April 2021

The cardia bifida in amphibians has the bulboventricular loop of the two hemi-hearts convex towards the mid-line. In birds the two loops have been reported to be convex towards the outside because all the experimental methods of producing cardia bifida in birds, unlike amphibians, impede the closure of the foregut.

The morphologic expression of each cardiac primordium was studied without altering endodermal tubulation or altering it only to the least possible degree. It has been demonstrated that the cardia bifida in birds has the two bulboventricular loops convex towards the mid-line and that the heart loops formed by only one primordium also tend to be convex towards the mid-line. Previous studies have been confirmed in the sense that the caudal portion of the left hemi-heart is the more prominent than the right one and that the left hemi-heart has faster heating rate than the right one until stage 12.

When the caudal portion of the left cardiac primordium was removed at stage 9 of Hamburger & Hamilton, in all cases a loop convex to the right was formed. This fact excludes that this portion of the left primordium is the origin of the right bending of the cardiac tube.
The origin of the epidermis in the supernumerary regenerates of triple legs in cockroaches (Blattaria)1
Authors: Bohn Horst
Published: April 2021

An attempt has been made to clarify the origin of the supernumerary regenerates of triple legs by transplantations between two species of cockroaches, Gromphadorhina portentosa and Leucophaea maderae. The three ways of combining stump and transplant tissues were: heteropleural, dorso-dorsal, antero-posterior (I); heteropleural, dorso-ventral, anteroanterior (II); homopleural, dorso-ventral, antero-posterior (III). The transplantations have been performed at the level of the tibia as well as at the level of the coxa.

(1) The supernumerary regenerates were partly mixed, i.e were composed of a mosaic of the tissues of both species of cockroach, partly homogeneously built up by the tissues of only one of the two species. In combination I nearly all regenerates were mixed; in the other two combinations homogeneous regenerates were relatively numerous, sometimes even the most numerous.

Both supernumerary regenerates of a triple leg might be mixed; or one was homogeneous and the second mixed; or they were both homogeneous. In the latter case one regenerate was built up by Gromphadorhina tissues, the other by Leucophaea tissues, or, more rarely, both were built by up Gromphadorhina tissues.

(2) The intraspecific transplantations simultaneously done in Leucophaea gave results which correspond in general with the results of the interspecific transplantations.

(3) From the composition of the supernumerary regenerates it must be concluded that the four different properties of a cross-section (anterior, posterior, etc.) are not yet determined irreversibly in the tissues of the cockroach legs. Thus, missing properties may be completed by the other properties to give an entire cross-section.
Experimental studies on the organization of the preimplantation mouse embryo:II. Reaggregation of disaggregated embryos
Authors: Stern M. Susan
Published: April 2021

The reaggregation and subsequent development of a range of disaggregated embryos has been examined:

Following complete dissociation embryos from 8-cell to late blastocyst reaggregated and developed to form morphologically normal blastocysts, even when blastomeres of two different developmental stages were present in the reaggregate. Dissociated mid-blastocysts could also reaggregate to form blastocysts but more commonly they produced vesiculated masses, as did disaggregates of late blastocysts. Successful fusion of pairs of mid or late blastocysts, with full cell numbers, was achieved following partial dissociation.

These results are discussed in relation to blastocyst formation. It is suggested that even if the embryo derives polarity from the oocyte it is not functionally essential to normal development in view of the remarkable regulative capacity of the egg.
The effect of spatial arrangement on cell determination during mouse development
Authors: Hillman N. , Sherman M. I. , Graham Chris
Published: April 2021

The effect of cell position on cell determination was studied in mouse embryos. Embryos and parts of embryos were combined during early preimplantation development. The differentiation of cells in these composites was followed either by prelabelling some cells with tritiated thymidine or by combining cells which synthesized different electrophoretic variants of glucose phosphate isomerase.

It was found that each blastomere of a 4-cell embryo could form both the trophoblast and the inner cell mass of the blastocyst. However, when blastomeres of a 4-cell embryo were placed on the outside of other 4-cell embryos then (a) they tended to form the outside layer of the blastocyst, (b) they tended to develop into the trophoblast and the yolk sac on the 10th day of pregnancy, (c) they tended not to form the coat colour of the foetus. Four-to eight-cell embryos which were completely surrounded by other blastomeres had lost the capacity to form vesicles at the blastocyst stage.

We could find no evidence for the segregation of morphogenetic factors at the 4- and 8-cell stages of mouse development and concluded that at these stages cell position could determine the development of blastomeres.
The appearance and quantitation of cytoplasmic ribonucleic acid in the early chick embryo
Authors: Wylie C. C.
Published: April 2021

This paper seeks to extend our knowledge about RNA synthesis in early embryogenesis to the domestic fowl, Gallus domesticus. Using this species for research, apart from increasing our knowledge of higher vertebrate embryology, has certain advantages such as rapid uptake of isotopic precursors and ease of microdissection in culture.

The following results are presented:

The cell number in the whole chick embryos is shown to be increasing logarithmically between the time of laying and the early neurula stage; with a doubling time of 7·4 h. The onset of ribosomal RNA synthesis has been shown to be during mid-cleavage of the chick embryo, while development is taking place in the oviduct and uterus of the mother. In a cumulative labelling experiment, embryos were labelled at the unincubated-egg stage, allowed to develop to various morphological stages up to neurulation, and their cytoplasmic RNA prepared and analysed by gel electrophoresis. The specific activity of the precursor pool for RNA synthesis was measured at several stages, using the same labelling conditions, and the results were used to quantitate the RNA synthesis from the incorporated radioactivity. Using these techniques, it was found that newly synthesized cytoplasmic RNA accumulates steadily in the whole chick embryo, reaching a level of 104 μg by the early neurula stage. On a per cell basis, however, the amount of newly synthesized cytoplasmic RNA seems to decrease slightly.

These findings are discussed in the light of present knowledge about embryos of other vertebrates and certain invertebrates.
Localization and growth pattern of the tergite Anlage of Drosophila
Authors: Santamaria Pedro , García-Bellido Antonio
Published: April 2021

Following cauterization in different regions of each larval segment, different effects - on growth and pattern - in the adult hemitergite were obtained. A correspondence between different segments in the larva and in the adult was found, with the exception of the Vllth abdominal segment in the male, which apparently has no adult cuticular representation. The histoblasts forming the imaginal Anlage are grouped in the central part of the larval hemisegment. Following cauterization, the viable histoblasts only partially replace the killed ones, giving rise to incomplete tergites.

Pattern damages are characteristic of the cauterized region. Cauterization in marginal regions of the abdominal segment, although not killing the histoblasts, induce specific fusions and penetrations between neighbouring colateral and contralateral hemitergites. The effects of cauterization on the number of cuticular elements and their disposition in the adult pattern are discussed.
Surface modifications of neural epithelial cells during formation of the neural tube in the rat embryo
Authors: Freeman Bruce G.
Published: April 2021

The apical (juxtaluminal) ends of the neural epithelial cells of rat embryos were examined using light and electron microscopy during varying stages of neural tube formation. At the neural-plate stage the apical surfaces exhibit numerous microvilli. At the presomite neurula stage the microvilli are longer and more irregular. Filaments of approximately 40–60 Å diameter appear in the apical cytoplasm. By the neural-groove stage, cytoplasmic protrusions containing various organelles have begun to appear. Apical filaments are present. At the beginning of closure the apical surfaces are characterized by large, irregular protrusions that are still associated with apical filaments. Finally, at the time of neural closure, the apical protrusions as well as the apical filaments have disappeared and the apical surfaces of the neural epithelial cells are relatively smooth.

These observations bear out the proposal that contraction of the apical filaments is responsible for the folding of the neural plate and the production of apical protrusions.
Development of protein polymorphisms in redwing blackbirds
Authors: Brush Alan H. , Scott Alan F.
Published: April 2021

Breeding populations of the redwing blackbird, Agelaius phoeniceus, were studied to compare protein differences during development. Proteins which represented a minimum of ten loci were studied in egg white, embryonic, nestling and adult tissue. In starch-gel electrophoresis at several conditions of pH only ovoglobulin, ovotransferrin and general esterases were polymorphic. Tissue specificity was observed in other isozymes. These data suggest that developmental sequences of proteins may be considered an adaptative response of the organism.
Modification of muscle cell phenotype in monolayer culture by different media
Authors: Ramírez Oscar , Alemán Victor
Published: April 2021

Conditions for monolayer cultures of chick skeletal muscle in a rich medium showed that non-muscle contaminants were only 20% of the population. Although the calcium content of this rich medium was 0·95 mM, multinucleate and long fibres were observed after 8 days in culture.

Either in rich or in restricted media, gelatin organized the pattern of cell and fibre development in the Petri plates. Cells grown outside the gelatin boundaries looked fibroblastshaped and many were vacuolated. Gelatin did not fully prevent the growth of fibroblast-like population.

Calcium in restricted media appeared to be very important for the acquisition of a definite elongated shape.

The possibility of the existence of myofibro-myoblasts was supported by the finding of multinucleated fibroblast-like cells during culture in restricted medium. Epigenetic factors, such as different media in a given culture or the origin of a serum batch utilized as a component of those media, affected the fate of the cultures and might also explain the myoblastic variance observed in this and other studies reported.

The capacity of phenotypic expression during the modulation change of muscle cells, in vitro, depends not only upon their genotypic origin but also on parameters such as the cell stage during this process, the type of nutrient media used and the interplay of both parameters; in vivo it depends upon specific cytological interactions.
The fine structure of the developing retina in Xenopus laevis
Authors: Dixon J. S. , Cronly-Dillon J. R.
Published: April 2021

The fine structure of the developing retinal cells in Xenopus laevis was studied from stages 26 to 36. At all stages examined the cells contained large numbers of free ribosomes, polysomes, small mitochondria, lipid and yolk droplets and scanty granular reticulum. A basal lamina covered the smooth internal margin of the optic vesicle and also the external aspect of the germinal pigment epithelial cells.

At all stages examined zonulae adhaerentes occurred between adjacent cells at the outer aspect of the optic vesicle and maculae adhaerentes diminutae were occasionally observed. A third type of intercellular junction, characterized by a narrow gap of 3–9 nm, occurred throughout the retina up to stage 30 but only at the periphery beyond this stage. It is suggested that the disappearance of these junctions from the central portion of the retina may be correlated with retinal cell specification* which is known to occur at stage 30–31. These junctions may represent sites for the cell to cell transfer of small molecules which are required for cell differentiation. Since new cells are continually being added to the retina from the ciliary margin beyond stage 30 the persistence of junctions in this region may explain how these new cells also become specified.*
Caudal regeneration in the absence of a brain in two species of sedentary polychaetes
Authors: Hill Susan Douglas
Published: April 2021

Evidence has been obtained showing that unlike the requirements of errant polychaetes studied by other investigators, at least two species of sedentary polychaetes, Branchiomma nigromaculata and Chaetopterus variopedatus can undergo caudal regeneration in the absence of a brain. Both Branchiomma, when maintained in a brainless condition by repeated removal of anterior segments, and Chaetopterus, when rendered brainless by amputation of cephalic segments at a level at which anterior regeneration does not occur, undergo posterior regeneration following removal of caudal segments. Animals maintained in a brainless condition for 7–10 days prior to posterior segment removal undergo normal posterior regeneration. Consequently, it appears unlikely that a circulating brain hormone present at the time of amputation is responsible. Experiments were performed on the extremely long 13th segment of Chaetopterus. An isolated posterior half of segment 13, which possesses ventral ganglia, regenerates both anteriorly and posteriorly, while the anterior half regenerates only anteriorly. That the tissues of the anterior half of segment 13 are competent to regenerate posteriorly was shown by leaving the anterior half of the segment attached to the first 12 segments. Under these conditions posterior regeneration occurred. These experiments suggest that the ventral ganglia rather than the brain are important in posterior regeneration in these species.
Les premiers stades de la formation de l’ébauche de nageoire pelvienne de Truite (Salmo fario et Salmo gairdnerí): I. Etude anatomique
Authors: Geraudie J. , François Y.
Published: April 2021

The first stages of genesis of the pelvic fin Anlage in the Trout (Salmo fario and S. gairdnerí). I. Anatomical study

The Anlage of the pelvic fins appears in Salmo 2 weeks after the fecundation day, at the level of the somites 23-26. The mesoderm has a double origin and seems to differ in this regard from the hind limb of most of the amniotes.

The ‘initial mesenchyme’ comes from the local proliferation of the somatopleura. It will give essentially the skeletal components of dermal origin (actinotrichia and lepidotrichia). The ‘secondary mesenchyme’ is obtained by the dispersion of four ventral somitic processes that have reached and entered the initial mesenchyme blastema. The secondary mesenchyme will probably give the muscles and also the endoskeleton of the fin. The origin of the girdle is not clear. When the setting of the initial mesenchyme begins the epithelium that covers the embryo is already differentiated in an epiderm with numerous mucous cells resting on a visible basement membrane. At the apex of the pelvic bud, a localized and transitory thickening of the epiderm is produced by the increase in the height of the basal stratum. We call this structure by the name of ‘pseudo apical cap’ to stress the fact that it must be distinguished from the ‘apical cap’ described for the limb bud of amniotes.

So, the morphogenesis of the pelvic fins of Salmo shows some important particularities in the epiderm as well as in the mesoderm.
Protein synthesis during Ilyanassa development: effect of the polar lobe
Authors: Teitelman G.
Published: April 2021

Removal of the polar lobe at the trefoil stage of the first cleavage division of Ilyanassa embryos causes abnormalities much later in development. To determine if the developmental differences between normal and delobed embryos were reflected in alterations in protein synthesis and at what stages of development these become evident, protein solutions were separated by disc electrophoresis on basic acrylamide gels. For the analysis of the newly synthesized proteins, two protein samples, one labelled with 14C and the other with 3H, were combined in the same electrophoretic column. Each was prepared from normal embryos or lobeless embryos at different stages of development.

The distribution of the two groups of differentially labelled proteins was compared by a determination, for each fraction, of the ratio of the normalized 3H/14C counts for that particular fraction (R =3H/14C). The plot of R versus fraction number was studied for various combinations of samples.

During normal development the profile of labelled proteins remains unchanged until the onset of visible differentiation. At this stage, around day 4 of development, there are changes in biosynthesis revealed by a greater emphasis on the synthesis of slow moving proteins. The profile of labelled proteins of lobeless embryos remains unchanged up to the 5th day of development. This result is correlated with the absence, in the lobeless embryos, of many of the visible differentiations.

Preliminary studies revealed that the spectrum of labelled proteins of the polar lobe is identical to the one present in lobeless embryos and in normal embryos in early stages of development. This suggests the possibility that the morphogenetic factors associated with the polar lobe are not among the newly synthesized proteins. A hypothesis is presented to account for the effects on morphogenesis and protein synthesis which are produced by removal of the polar lobe.
Morphogenetic disturbances from timed inhibitions of protein synthesis in Fundulus
Authors: Crawford Richard B. , Charles E. Wilde , Heinemann Murk H. , Hendler F. J.
Published: April 2021

The reversible inhibition of protein synthesis at the 75 –95% level in the early zygote of Fundulus results in a specific series of developmental failures dependent upon the times of inhibitor pulse initiation. The severity of the morphogenetic failure is inversely related to the time of initiation and directly to the length of the pulse. The defects reflect the time dependent serial order of events in morphogenesis. The defects range from failure of cleavage through disorders of blastulation, failure of axiation, anencephaly to microcephaly and are entirely predictable. With the exception of cleavage failure the pattern is identical with that found using pulses of actinomycin D in a similar manner. The agent used was pactamycin, an antibiotic which reversibly inhibits amino acid incorporation into protein by disturbing the assembly of the functional ribosomal complex. The significance of time dependent protein synthesis as an active expression in morphogenesis of similarly time dependent information flow via RNA synthesis is discussed.
Effect of a proline analogue, azetidine-2-carboxylic acid, on the morphogenesis in vitro of mouse embryonic lung
Authors: Alescio T.
Published: April 2021

A proline analogue, azetidine-2-carboxylic acid, which has been reported to selectively depress collagen biosynthesis, affects lung morphogenesis in vitro by determining differential modifications of the rate of epithelial growth and ramification activity.

Low concentrations of the analogue induce a sharp decline of the number of newly formed terminal buds, leaving the rate of global growth of the epithelial tree almost unaffected. This effect is reversed by increasing doses which appear more effective on global epithelial growth than on budding. DNA and protein content at the end of the treatment are unequally reduced. Protein concentration is more depressed with consequent rise of the DNA/protein ratio.

These results show that epithelial budding is very sensitive to the treatment with the analogue, and draw attention to collagen biosynthesis as one of the possible mechanisms by which the mesenchyme controls the spatial organization of the epithelial tree. This type of control appears relatively independent on the actual rate of epithelial cell replication, since budding is much more sensitive to the action of the drug.
Effects of erythropoietin on cell populations and macromolecular syntheses in foetal mouse erythroid cells
Authors: Paul John , Conkie David , Burgos Hugo
Published: April 2021

The effects of erythropoietin on maturation of erythroid cells were studied in short-term cultures of foetal mouse liver. Erythropoietin-treated cultures had about 50% more cells than untreated cultures after 24 h. The increase occurred in basophilic, polychromatic and orthochromatic erythroblasts as well as in reticulocytes. A striking feature of erythropoietintreated cultures was the formation of macro-erythroblasts and macrocytes. Autoradiographic studies indicated that a maturation division was omitted in the formation of these cells and that macrocytes might be derived directly from polychromatic erythroblasts or earlier stages. These studies also indicated that there might be no more than three divisions during the normal development of orthochromatic erythroblasts from proerythroblasts in vitro. The mitotic index of proerythroblasts was raised in erythropoietin-treated cultures within 1 –2 h. Moreover, erythropoietin caused a marked elevation of DNA synthesis in proerythroblasts within the first hour of culture but effects on DNA synthesis in other cell compartments were not pronounced. In contrast, an increase in RNA synthesis was noted in proerythroblasts and basophilic and polychromatic erythroblasts; it was greatest in the two former compartments. The stimulation was noticeable, especially in the basophilic compartment, within 2 h but increased progressively throughout the first 5 –6 h. Erythropoietin did not induce an increase in total protein synthesis in cells of the normal series but macro-erythroblasts exhibited proportionately more grains.
The Effects of Ultrasonic Treatment on Embryonic Development of Drosophila melanogaster
Authors: Counce Sheila J. , Selman G. G.
Published: April 2021

The use of ultrasonics as a tool for the experimental study of embryonic processes in Drosophila has been investigated. It has been found that developmental changes can be induced by the application of ultrasonic waves at intensities sufficiently low to obviate the possibility of cavitation damage or chemical change. The effects of ultrasonic waves of various intensities on different developmental stages has been studied by direct visual observation during treatment and in permanent preparations of sectioned material at subsequent developmental stages. Treatment at preblastodermal stages was usually followed by readjustment and normal but delayed development; in other cases death ensued without further development. Treatment of eggs in late cleavage stages with ultrasonic intensities of 0·5 to 1·2 watts/cm.2 for 30 seconds produced abnormalities of spindle, displaced centrioles, and induced polyploidy. Treatment at the syncytial blastoderm stage, with ultrasonic intensities 0·3 to 0·5 watts/cm.2 for 30 seconds, resulted in the production of a high proportion of developmental abnormalities which were classified into five different categories: (a) death without further development; (b) proliferation of cells without differentiation; (c) differentiation without organization; (d) abnormal organization; and (e) slight abnormalities in organization. The possible causes of the different types of abnormalities in embryonic development after treatment with ultrasonics are considered, and are discussed in relation to abnormalities in embryogenesis which have been produced in Dipteran embryos by other means, and in the light of the general morphogenetic situation existing in Diptera and certain other insect orders. Further applications of the method to developmental studies are suggested.
Nitrogen-Excretion in Carcinides maenas (Pennant) during the Early Stages of Regeneration
Authors: Needham A. E.
Published: April 2021

Amputation of appendages in fasting Carcinides causes an immediate large increase in nitrogen output which then declines along an exponential type of curve, during the next 12 days or so. Superimposed on this curve are cyclic fluctuations in output, with a period of about 6 days. The excess output over the first 10 days is proportional to the normal output before operation, the relative excess being independent of diet. Later, however, carbohydrate reduces output and protein increases the short-term oscillations in output. Excess nitrogen output is related to the amount of damaged tissue remaining but not to the amount of tissue removed. It is not due entirely to the nitrogen from demolished tissues. Removal of the sinus gland region of the eye-stalks causes an increase in output greater by one order of magnitude than that due to limb-amputation. By contrast, amputation of the tips of the eyes only depresses output. Extirpation of the second antennae depressed output slightly, probably indicating that the antennal gland normally excretes nitrogen. After excision of portions of the body-wall the pattern of output differs from that following amputation of appendages, and is more similar than the latter to that following skin and bone trauma in mammals.
On the Nature of Head Malformations Obtained by Centrifuging the Eggs of Limnaea stagnalis
Authors: Raven Chr. P. , Beenakkers A. M. TH.
Published: April 2021

Eggs of Limnaea stagnalis were centrifuged at a late 4-cell stage for 10 minutes at a centrifugal pressure of 925 × gravity. The head malformations produced by this treatment were studied. No cyclocephalic malformations were obtained. Apparently centrifuging does not produce a depression of the animal gradient-field. No median reduplications with a splitting of the apical plate were found. Hence centrifuging does not cause a strengthening of the animal gradient-field either. Lateral reductions of eyes, tentacles, and cerebral ganglia were obtained in a large percentage of the cases. They were equally distributed between both sides of the head. The frequency of lateral reductions decreases in the order: eye, tentacle, cerebral ganglion. Lateral eye reduplications occurred in a certain number of cases. They were not accompanied by a reduction of the velum. A complete splitting of the foot in two lateral halves was found in one case. The most characteristic effect of centrifugation consists of the formation of a supernumerary cerebral plate in an abnormal place. This may lie wholly in the post-trochal or in the pre-trochal region, or on the boundary between the two. As the supernumerary cerebral plate approaches one of the ‘host’ cerebral plates, the differentiation of the latter is more and more suppressed. Finally, the supernumerary plate may almost altogether supersede and replace one of the normal cerebral plates. The formation of a supernumerary cerebral plate cannot be explained by a disturbance of the animal gradient-field. The supernumerary plate appears to be superimposed upon a relatively undisturbed pattern of head organs. It is concluded that the normal pattern of head organs is controlled by a gradient-field located at early cleavage stages in the relatively immovable cortical layer. The differentiation of the cerebral plate, on the other hand, is dependent on a morphogenic substance which may be displaced by centrifugal force. In normal development, some kind of interaction between morphogenic substance and gradient-field takes place. The most simple hypothesis appears to be that the localization of the ‘cerebral plate substance’ during ooplasmic segregation is controlled by the cortical gradient-field.
The Site of Implantation of Ova in the Rat
Authors: Frazer J. F. D.
Published: April 2021

In the rat, implantation sites on the 9th day of pregnancy were only evenly distributed along the uterine horns when there were 5 or more ova in one horn. With lesser numbers ova tended to implant in the caudal end of the horns.
Malformations déterminées par des injections de substances chimiques localisées à la tête d’embryons de poule
Authors: Ancel par P.
Published: April 2021

Nous avons cherché à montrer dans des travaux antérieurs (Ancel, 1954) sur l’embryon de Poule, l’utilité des injections localisées en chimiotératogenèse, en particulier pour la réalisation de malformations n’existant pas à l’état spontané chez les Oiseaux comme la symélie ou rares comme l’ectrosomie. La réalisation des malformations de la tête qui fait l’objet de ce mémoire s’ajoute à ce sujet à nos résultats antérieurs. Les injections localisées à la tête d’embryons de Leghorn blanches ont été faites à l’aide d’un appareil spécial (Ancel & Rouget, 1954). Elles ont été réalisées dans les conditions suivantes.
The Development of the Ultimobranchial Body in Xenopus laevis Daudin and its Relation to the Thyroid Gland and Epithelial Bodies
Authors: Saxén Lauri , Toivonen Sulo
Published: April 2021

The authors have investigated the formation and normal development of the ultimobranchial body and its ability to store iodine in Xenopus laevis Daudin. In this species the ultimobranchial body develops from the base of the sixth visceral pouch and forms laterally to the larynx a paired organ in which a limited number of distinct follicles are seen. The organ is formed at the beginning of metamorphosis, attains its maximal size in the middle of it, and partially degenerates at the end of metamorphosis. On the basis of the results presented it is suggested that the ultimobranchial body has its own specific secretory activity, which is evidently most highly developed during metamorphosis and weakens thereafter. Investigations with radioactive iodine (I131) have shown that the organ does not act as a thyroid gland. Neither does the ultimobranchial body form thyroid tissue or accessory epithelial bodies (parathyroid glands) during development.
On the mechanism of determination of embryonic polarity in Parascaris and Rhabditis
Authors: Tadano Yanagi , Tadano Masashi
Published: April 2021

In an attempt to explain the determination mechanism of embryonic polarity, the relation between the behaviour of ectoplasm and the turning of the P2-cell in embryo sof Parascaris equorum, Rhabditis ikedai and Rhabditis sp., has been studied by means of centrifugation.

During cleavage of uncentrifuged eggs, extension and contraction of the cell-surface occur. These are accompanied by streaming of the ectoplasm. In the early phase of the second cleavage embryos become T-shape. Along with streaming of ectoplasm at the animal side of S2-cell in the later phase, the surface of S2-cell extends on one side and contracts on the other. Successively, P2-cell turns from the extending side of S2-cell to the contracting one, that is, in the direction of the primary streaming of ectoplasm. Thus, the embryos become rhomboidal in shape and their axes are established. The extended side of S2-cell points roughly to the ventral side of the embryo, and the other to the dorsal.

In the centrifuged embryos, extension and contraction of cell-surfaces and turning of P2-cell take place also accompanied by streaming of the ectoplasm at the centrifugal side of S2-cell.

It is concluded from these facts that the determination of embryonic polarity depends on the turning of the P2-cell by the extension and the contraction of the surfaces of S2-cell and that the direction of this turning depends on that of the primary streaming of ectoplasm in S2-cell. It is assumed that the direction of the streaming is due to the migration of the nucleus, and that the extension and contraction of cell-surfaces is based on the behaviour of the E.R. and microtubules in the ectoplasm. The tetrahedral embryo is caused by a change in the streaming of ectoplasm. The formation of a rhomboidal embryo in Rhabditis without a preceding T-stage is discussed in connection with the behaviour of the ectoplasm.
A quantitative analysis of the effect of excision of the AER from the chick limb-bud
Authors: Summerbell Dennis
Published: April 2021

The effect of removal of the apical ectodermal ridge from the early chick limb-bud is re-examined using a new quantitative method of analysis of results. The concept of the proximo-distal sequence of laying down of parts is confirmed and evidence is presented that this proceeds as a continuous process, there being a gradual change in the level specified from one cell to another at a more distal level. The results are then interpreted in terms of the ‘progress zone’ model to show that they are both consistent with the model and that they provide an assay for one of its parameters, the rate of change of positional value with time at the tip.
The site of action of the ichthyosis locus (ic) in the mouse, as determined by dermal-epidermal recombinations
Authors: Green Margaret C. , Alpert Barbara N. , Mayer Thomas C.
Published: April 2021

Skin of 14-day ic/ic and +/+ embryos was separated into dermal and epidermal layers using trypsin, and recombined in the combinations + / + epidermis with + / + dermis, + / + epidermis with ic/ic dermis, ic/ic epidermis with +/+ dermis, and ic/ic epidermis with ic/ic dermis. The recombined tissues were implanted in adult histocompatible testes and allowed to grow for 2 weeks. The type of hair that developed in the grafts corresponded to the genotype of the epidermis, and was not influenced by the genotype of the dermis. We conclude that the ic locus acts in the epidermis.
Potentialites hématopoïétiques de tissus embryonnaires et adultes analysees par greffe à des poussins irradiés
Authors: Samarut Jacques , Nigon Victor
Published: April 2021

Differentiation of haemopoietic tissues from embryos and adults injected into irradiated chickens

Irradiated chicken are injected with haemopoietic tissues from adult or 11-day-old embryos. Development of stem cells gives rise to well-defined erythrocytic colonies on the surface of the tibial marrow. Erythropoietic production appears to be similar from adult marrow and embryonic blood stem cells; production from injected vitelline stem cells seems to be between 3 and 4 times higher than that of adult marrow stem cells. Results are discussed on the basis of two hypotheses:

–existence of an extramedullary erythropoietic site in the host after vitelline cells grafting;

–development of vitelline stem cells in the host marrow with kinetic patterns different from those of grafted adult marrow or embryonic blood stem cells.

Anyway, the 11-day-old embryo appears to contain at least two types of blood stem cells with distinctive properties. Developmental origin, relationship and future of these different stem cells remain to be analysed.
Rôle du mésoderme somitique dans le développement de la cage thoracique de 1 embryon d’oiseau. I. Origine du segment sternal et mécanismes de la différenciation des côtes
Authors: Chevallier Alain
Published: April 2021

Role of the somitic mesoderm in the development of the rib cage of bird embryos

I

Origin of the sternal component and conditions for the development of the ribs

The developmental origin of the sternal component of the ribs and the conditions for the development of the rib cage have been elucidated in bird embryos.

Experiments consisted in homo-or heterospecific transplantations of 2-day-old quail or chick embryo somitic mesoderm into chick hosts of the same age in ortho-or heterotopic position along the cephalo-caudal axis.

Results show that vertebral halves, ribs (not only their vertebral segment, but also their sternal component when they possess one), the trunk and intercostal muscles, as well as at least part of the scapula originate exclusively from the somitic material, while the sternum, ventral muscles and the other parts of the pectoral girdle are derived from the somatopleural mesoderm.

The development of the rib basket is subjected to following rules:

—only the somitic mesoderm of the prospective thoracic region (somites 19–26) is able to give rise to ribs.

—only the somitic mesoderm of the posterior thoracic region (somites 22–26) is able to develop ribs with a sternal component.

—the vertebral component of ribs can develop outside the thoracic region.

—contrariwise, the sternal component can form only in the vicinity of the sternal anlage, i.e. within about three somites in front and rear of the normal limits of the thoracic region.

It is concluded that the somitic mesoderm is already regionalized at a stage slightly pre-ceding its metamerization and that the somatopleural territory of the sternum plays a morphogenetic role in the development of the sternal component of ribs, although it does not make a cellular contribution to their construction.
Différenciation in vitro de cartilage à partir des crêtes neurales céphaliques chez Pleurodeles waltlii Michah
Authors: Corsin Jacqueline
Published: April 2021

In vitro differentiation of cartilage from cephalic neural crest of Pleurodeles waltlii Michah

Parts of cephalic neural crest of Pleurodeles waltlii have been cultivated in vitro alone or in explants containing other cellular components. It was hoped that these experiments would establish under what conditions cephalic neural crest cells can differentiate into chondroblasts. It has been demonstrated that this differentiation is possible only under the influence of the dorsal mesoderm and foregut endoderm.

It appears that neural crest cells are relatively pluripotent and progressively differentiate in response to local environmental factors.
Limb development in mouse embryos: protection against teratogenic effects of 6-diazo-5-oxo-L-norleucine (DON) in vivo and in vitro
Authors: Greene R. M. , Kochhar D. M.
Published: April 2021

The glutamine analogue, 6-diazo-5-oxo-L-norleucine (DON), has been shown to inhibit biosynthesis of purines and glycosaminoglycans, presumably by blocking the glutaminedependent steps in the biosynthetic pathways. The teratogenic potential of DON on the developing mouse limb-bud in vivo and in vitro was studied in an attempt to discriminate whether DON is exerting its teratogenic effect by interfering with glycosaminoglycan or purine metabolism.

A single intramuscular injection of DON (0·5 mg/kg) to ICR/DUB mice on day 10 of gestation resulted in 76% resorption, while fetuses surviving to day 17 exhibited growth retardation, median cleft lip, and limb malformations. Concurrent administration of L-glutamine (250 mg/kg) provided no protection against resorption or malformations, while 5-aminoimidazolecarboxamide (A1C, 250 mg/kg) decreased the resorption rate to 34% without significantly altering the incidence of malformations. Injection of DON alone on day 11 resulted in 87% of fetuses exhibiting limb malformations, with only 2% resorption. Concurrent injection of A1C decreased the frequency of limb malformations to 32%. L-Glutamine, D-glucosamine, or inosinic acid were without any protective effect in vivo.

DON (5 µgml medium) added in vitro to organ cultures of day 11 mouse limb-buds caused all limbs to evidence cartilage abnormalities. In this system, either L-glutamine or D-glucosamine (0·5 mg/ml medium) provided protection against DON effects while A1C (0·5 mg/ml medium) offered no protection in vitro.

These data suggest that DON exerts its effects in vivo by interfering with purine metabolism while in vitro its teratogenic action may be interruption of glycosaminoglycan biosynthesis. This may reflect upon the relative importance of growth and differentiation to limb development in vivo and in vitro. These data infer that limb development in vitro relies more on the differentiative process (differentiation of cartilage) than on growth, whereas limb development in vivo is dependent, at this stage, to a greater extent on growth for normal phenotypic expression.
The distribution of non-synaptic intercellular junctions during neurone differentiation in the developing spinal cord of the clawed toad
Authors: Hayes Brian P. , Roberts Alan
Published: April 2021

The distribution of intercellular junctions, other than synapses and their precursors, has been described in the developing spinal cord of Xenopus laevis between the neurula and free swimming tadpole stages. At the neurocoel, ventricular cells are joined in the apical contact zone by a sequence of junctions which usually has one or more intermediate junctions but often also includes close appositions, gap junctions and desmosomes. This apical complex is more diverse than that reported in other vertebrate embryos and between ependymal cells in the adult central nervous system. Gap junctions are also found between ventricular cells and their processes near the external cord surface. However, no other special junctions occur in this location under the basement lamella which surrounds the cord. Punctate intermediate junctions are generally distributed between undifferentiated and differentiating cells and their processes but were not found in neuropil after stage 28. These results are discussed in relation to cell movements during neural differentiation, possible effects on the freedom of movement of ions and molecules through extracellular pathways in the embryo, and possible inter-cytoplasmic pathways via gap junctions which may be responsible for the physiologically observed electrical coupling between neural tube cells.