Report - Carnegie Year Book 37

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George Linius Streeter (1873-1948)

Carnegie Institution of Washington - Year Book No. 37

July 1, 1937 - June So, 1938

Published By Carnegie Institution Of Washington

Washington, D. C. 1938

Department Of Embryology

George L. Streeter, Director (1938)

Address: Wolfe and Madison Streets, Baltimore, Maryland.

Contributions to Embryology

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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Early Stages Of The Primate Embryo

The Eight-Day Primate Egg

In Year Book No. 33 a report was given of the obtaining of a 10-day macaque embryo and it was pointed out that our vision of the mechanism of development was thereby extended into the 24-hour period preceding any hitherto known primate ovum. The year following we were able to report two 9-day specimens, one just before implantation and one just in the process of attaching. With these two eggs the known territory was extended another 24 hours earlier. During the past year we have obtained an 8-day ovum and again a still earlier 24 hours has been mastered. This carries us back to where, in its histological structure, the primate ovum is close kin to other mammalian forms, and to where they have in common the developmental pattern of a blastocyst. It is of the greatest importance that we have acquaintance with this expression of their common unity in functional requirements and the common way they have of meeting them. In going back to origins, once this unity is arrived at, any of the earlier developmental phenomena are in large part common to all mammals and we can in those early periods study them in any order, genus, or species that suits our convenience.


The 8-day ovum of the macaque consists of a blastocyst having a diameter of 0.175 mm., still enclosed by a disintegrating zona pellucida. This unique specimen was reported upon by Dr. C. H. Heuser before the American Association of Anatomists. An outstanding feature of it is the fact that at the embryonic pole there are still a few cells that are approximately double the size of the others. It is clear to see that they have not divided so many times. These relatively inactive cells appear to be the ones that are destined to form the embryo proper. They are large, few in number, not oriented in position, and show no tendency to unite into a common structure, all of which are characteristic of primitive blastomeres. In contrast to these primordial cells, the other cells are numerous, small, and are rapidly differentiating into special structures which will serve to attach the ovum to the uterus and eventually provide the contained embryo with its nourishment and other physiological requirements. In the point of sequence the stage is set before the embryo makes its appearance. In this blastocyst Dr. Heuser finds that he can see clearly that the materials of the ovum have, already on the eighth day, been segregated into the embryonic and extra-embryonic, or auxiliary, parts of the ovum. Thus the eighth day may be said to mark the completion of the first and hence the most fundamental chapter in the development of the ovum.


Implantation

The second chapter in the history of the ovum is its attachment and implantation in the endometrium of the uterus. But this is a long and complicated process overlapping the subsequent stages and so is not exactly a chapter. Implantation must begin, however, and establish its initial principles before growth and development of the ovum can ensue. Some phases of this process have been described in previous reports. During the past year a study of placentation in the macaque has been brought to a conclusion by the author in cooperation with Dr. G. B. Wislocki and published in its completed form. The study is based on a series of stages representing an almost day by day record from the ninth day when the egg first fastens, through the early and formerly least-known phases of placental development, up to the 35th day, by which time the mature features of the placenta are attained. In fact this constitutes the only relatively complete record in existence of the development of this fetal structure in any primate. The earlier stages are quite unknown in the gibbon and the anthropoid apes and in man our knowledge is fragmentary concerning all events preceding the 14th day.


From the biological standpoint the phenomenon of implantation is of peculiar interest. Here we have the ovum as a minute living organism attaching itself to the surface epithelium of the uterus and, after inducing both stimulative and degenerative changes in it, we see the ovum ingest this altered epithelium, with a corresponding increase in its own mass. The whole picture of this act of parasitism can be followed in its finer cytological details and one can determine the microscopic characteristics of the surrender of one living tissue to another. During the first two weeks this ingestion of maternal cells and intercellular plasma provides the sole source of growth material for the embryo and for a long time it overlaps the materno-fetal vascular exchange which, to a large extent, gradually replaces it.


The placental development is found to pass through three general periods or stages. The first of these is the prelacunar stage, in which trophoblast cells of the ovum erode and ingest the maternal epithelium at the implantation site and thus come in direct contact with the uterine stroma. While this is happening the maternal epithelium of the surrounding area proliferates, thereby building more pabulum for the trophoblast cells to fatten on. Within 24 hours a thick trophoblastic plate is formed at the embryonic pole of the ovum, sealing in the gap created by the disappearance of the maternal epithelium.


A second stage follows during which the trophoblastic plate, in continuing to thicken, develops lacunae into which the maternal capillaries empty and promptly fill with plasma and red cells. These spaces greatly increase the absorptive area and there is a corresponding increase in the amount of trophoblast. The very rapid growth of trophoblast that takes place in three days is shown in the figure on page 6, where B to D represent the prelacunar stage and E to H represent the second or lacunar stage. The third or villous stage follows directly after the above stages. In the available material one can plainly follow the formation of the chorionic villi and the differentiation of cytotrophoblastic columns, the centers of which become transformed into reticular connective tissue and capillary-forming cells and thus compose the cores of the villi. The details of this transformation were previously described by Dr. Hertig as referred to in a previous report (Year Book No. 33). The villous stage begins about the 15th day and progresses to the completion of the placenta, the most important features of which can be seen already on the 35th day.


Carnegie Year Book 37 fig01.jpg

Fig. 1. Drawings illustrating the enormous growth that occurs in the trophoblastic wall (solid black) of the ovum in the four days following its parasitic attachment to the uterus. Tissue materials are necessary for such growth and these are supplied by the luxuriant uterine epithelium and the plasma and blood cells of the adjacent tissues. Previous to attachment there is very little actual increase in the mass of the ovum. These eight stages are all from monkey embryos shown at the same enlargement (X 75). Their ages are as follows: A, 9 days; B, 9 days; C, 10 days; D, 10 days; E, 10% days; F, 11 days; G, 12 days; H, 13 days.

Yolk-Sac and Gut Endoderm

Following the attachment of the ovum on the ninth and tenth days we can speak of the third chapter in its development. With the auxiliary parts of the ovum well on their way to differentiation there is an awakening of the cells that are to form the embryo proper. This awakening is expressed by their increase in number and by their orientation and arrangement into an ectodermal disk or embryo disk. In this process the disk becomes set off, both dorsally and ventrally, by fluid-containing spaces from the abutting auxiliary tissues. The exact time relationships vary a little in different specimens and still more so in different mammals, so that in the early stages the appearance at the embryonic pole may be quite different, but apparently the underlying principles remain the same.


During the past year the studies of the writer have been directed more especially to the fluid space which develops ventral to the embryonic disk. Whereas the dorsal space enlarges to become the amnion, the ventral space enlarges to become the combined gut and yolk-sac cavity. The yolk-sac is definitely something more than an embryonic vestige. Furthermore it does not bud off from the inner cell mass in the form of a solid clump of cells, thereafter acquiring a central cavity, as had been supposed. Nor is it at any time an intrinsic part of, or homogeneous with, the gut tract. Instead our specimens show us that the earliest cells of the yolk-sac are differentiated from the primitive endoderm as a thin membrane between which and the gut endoderm there arises the conjoint yolk-sac cavity and gut cavity.


This cavity ventral to the embryo disk is therefore dual in origin. It is bordered on its dorsal part by cells that are to form the gut endoderm, an induced product or migratory element from the disk itself; whereas the space on its ventral part is bordered by the yolk-sac endoderm, which is a derivative of the primitive endoderm and is in fact an auxiliary tissue. The gut and yolk-sac are thus different in origin and are always abruptly demarcated from each other. The one becomes a definite part of the embryo and the other is an auxiliary organ which in primates plays a temporary but apparently very essential role in the metabolism of the embryo up to that time when its functions are taken over by the placenta, a much more elaborate and efficient organ. Thereafter the yolk-sac regresses, although we can usually find its degenerate remnants attached to the fetal membranes at birth.

Young Human Embryos

Among the publications in the last number, volume 27, of the Contributions are three accounts of presomite human embryos. This early period of human development is imperfectly known because of the scarcity of well preserved normal specimens of that age, upon which our understanding must be built. One of these specimens is that of Dr. J. I. Brewer studied in the Anatomical Laboratory of the University of Chicago. This 15-day specimen is certainly normal and is in a good state of preservation and is destined to take its place as a standard 6f orientation in the procession of stages through which the human embryo passes in its development.


A slightly younger specimen has been studied in this laboratory by Dr. E. M. Ramsey. This specimen, known as the Yale Embryo, is estimated to be between 13 and 14 days old. It was obtained at autopsy and a sufficiently large block could be made to show fully the relations of the embryo to the uterine wall. Neither this nor the Brewer specimen has the perfection in histological detail that we are able to secure in our macaque embryos, and neither of them can be relied upon for some of the problems that involve finer cytology and intercellular reactions. The student of human embryology, however, is accustomed to such deficiencies and has been able to piece together his story from specimens, some of which are much less perfect than these. It is to be remembered that at the end of the second week even the gross general anatomy of the human embryo is still more or less obscure.

Among other things Dr. Ramsey analyzes the phenomenon of blood-sinus formation around the newly implanted ovum. The Yale specimen illustrates this particularly well and apparently it always occurs in normal specimens as soon as decidua appears. The sinuses are found to consist of localized dilatations of precapillary venules and their formation is an expression of the marked response that occurs in the endometrial vessels under varying hormonal and environmental conditions. Whether such localized allocations of blood plasma and red cells serve a nutritional function for the ovum or whether the sinuses are a means of lowering blood pressure in the vessels communicating with the lacunae, thereby shielding the embryo from pressure extrusion, remains to be determined. Perhaps the most important part of Dr. Ramsey's study is her analysis of trophoblast development, and her conclusion that there is a normal correlation between it and the decidua and the embryo proper. With the normal variation in these correlations established one is then in a position to recognize the abnormal. It is also noted that it is normal for the trophoblast to develop more luxuriantly on the deeper hemisphere of the ovum where the food is more abundant than on the side toward the uterine cavity. This is responsible for the apparent invasion inward. Besides the correlated growth of the trophoblast relative to other things, there is a regulation of its differentiation into syncytium on the surface and into primitive mesoblast on the inner side, the more primitive cytotrophoblast, later known as Langhans cells, being the germinal bed for both of them. Normally a balance is maintained between these elements. The occurrence of an imbalance between them in a specimen is evidence that it is pathological. Dr. Ramsey illustrates this by a specimen from the Carnegie Collection in which the supply of parent cytotrophoblast is exhausted, being wholly converted into mesoblast on one side and syncytium on the other.


The occurrence of "syncytial wandering cells" in the above specimen has given Dr. Ramsey an opportunity to analyze their origin. There is some evidence that these are not fetal cells but are transformed stroma cells, which are in the process of being converted into pabulum for the advancing trophoblast. On that basis the multinuclear or giant cell character could be regarded as an expression of degeneration. On the other hand, the distribution of the cells and the absence of other signs of degeneration leave the matter in some doubt. Dr. Ramsey's study of this phenomenon serves to call attention to a phase of implantation that has been largely overlooked.


A third human embryo, younger than either of the former, has been studied by Dr. E. Scipiades, Jr., of Budapest, a guest of this laboratory as an exchange student of the Institution of International Education. This specimen carries special interest because of an associated clinical history of hormone and "small dose" X-ray treatment for sterility. The embryo was discovered in curettage material and fortunately the sections pass through the ovum in a direction that discloses the implantation details. The trophoblast is primitive in character and as yet there are no villi. This places the specimen in the group of very early ones.

Organogenesis

The studies of Dr. E. H. Norris on the parathyroid and lateral thyroid glands will already be familiar to the readers of our embryological reports. There is now to be added to these a reference to his study of the human thymus gland, to which his investigations were extended. Part of his work was done on the embryological collection in Dr. Jackson's laboratory and part on our own collection.

In his study of the morphogenesis of the thymus Dr. Norris comes to conclusions which diverge somewhat from those of Dr. Weller, who also had worked in our laboratory and on the same material. This is wholesome and tends eventually to bring us nearer to the correct solutions of these questions. A point emphasized is the cervical sinus, which Dr. Norris concludes to be the primordium of the primitive thymic cortex and the source of Hassall's corpuscles, two very important assignments. Dr. Weller had concluded that the cervical sinus is a product of the mechanical exigencies of the region and is influenced by, rather than being the cause of, the development of the thymus. It is clear that much study is still needed throughout the region of the branchial pouches before we can unravel its many factors in development. It may be that some help can be obtained through experiment. The branchial clefts have been so heavily loaded with the philosophy of recapitulation that it is difficult to separate out what is the real gill-cleft phenomenon from what is the expression of other developmental factors of the region. It is possible that recapitulation in our ways of thinking is more inexorable than it is in the development of the embryo.

In his conclusions Dr. Norris derives the epithelial elements of the human thymus from two distinct sources both of which are within the third branchial complex. These two sources make it an ectodermal-endodermal structure. The ectodermal source is the cervical sinus, which provides the primitive thymic cortex and the HassaH's corpuscles, as noted above. The endodermal thymus, arising from the third endodermal branchial pouch, gives origin to the syncytial cytoreticulum of the gland. The thymic lymphocytes he finds to be of mesenchymal origin, secondarily invading the gland. Other elements of gland reticulum are derived from connective tissue cells in the adventitia of vessels and from the gland capsule.


Embryologists have utilized the somites very largely as a topographical scale against which the levels of the body are oriented. One difficulty has been the determination of the first or most oral somite, with which they must begin their count. There has been an uncertainty as to whether the first somite of a later stage is the same as the first somite of the earlier stages; that is, are new somites added in front or perhaps does the original first somite disappear? Either of these events would alter the count. An important study covering a survey of these occipital somites in a large number of human embryos has been made by Dr. L. B. Arey of Northwestern University, and the results were reported in the last volume of the Contributions to Embryology. He finds that the first pair of somites usually undergo regression both in size and in structure. By tracing this regression he concludes that dedifferentiation plays a considerable part in the process. The regression may be slow in some cases but usually in embryos of more than 20 somites the first remaining pair are actually second somites. Retarded differentiation and beginning regression can be made out as early as embryos of between 5 and 9 somites. For students of embryonic anatomy Dr. Arey's careful work in this field will be of importance. Also it adds to the general principles of development an instance of over-induction, eventually corrected by the lack of supporting stimuli.

In studying the anatomy of the whale fetus Dr. R. Walmsley has covered a field in which comparatively little systematic work had been done. Although of peculiar interest because of its high degree of specialization, the adult animal from its very size and its inaccessibility has rarely been available for study except in its skeletal form. In the fetus some of the difficulties are obviated and the opportunity of studying four fetal specimens has been well utilized by Dr. Walmsley not only to cover the fetal stages but through them to interpret the conditions and problems of the adult. His oldest specimen was a mid-term fetus, and the other three fell within the first half of pregnancy.

The respiratory mechanisms of the whale in adaptation to its habits of submergence have been of great interest to the anatomist and they have resulted in highly specialized structures that are foreign to other mammals. The most striking peculiarities of the whale, however, are found in its vascular system. Dr. Walmsley's investigations were largely concerned with this system. He made a systematic study of the blood vessels throughout the whole body, both as to their gross anatomy and as to their histology. A striking generalized characteristic of the arteries was the breaking up of what in other mammals would be a single trunk into a series of collateral vessels, a condition adapted to a large volume of total blood together with a low blood pressure. The feature of greatest interest was found to be the retia mirabilia, especially the thoracic, which is associated with decrease in lung volume during submergence, and the cerebrospinal retia, which serves as buffer interposed between the arteries of the main parts of the body and those intrinsic to the central nervous system. Dr. Walmsley concludes that these peculiarities of the whale vascular system are not provisions against a possible shortage of oxygen, for apparently such a shortage does not occur. Instead, this highly specialized system is an adaptation to the differences of surface pressure under which their mode of life requires them to live. It is thus understood why these specializations are more elaborate in the adult than in the fetus and are largest in whales that can remain submerged longest.

Physiology of the Embryo

Secretion in the Fetal Chorioid Plexus

Continuing his studies on the origin of function of the chorioid plexus in the fetal brain, Dr. L. B. Flexner with the cooperation of Dr. R. D. Stiehler has been able to show that the appearance of secretory activity of this plexus is correlated with the development of a difference of potential between stroma and epithelium and the initiation of an electric current between the two tissues. It had previously been shown that cerebrospinal fluid changes from an ultrafiltrate to a secretion at the end of the first third of pregnancy in the pig. In the new studies attention is turned to the biochemical changes that occur in the plexus at this transition period, when the plexus is changing from a passive state to an active chemical machine.

For determining the potentials of epithelium and stroma use was made of oxidation-reduction indicators and it was found that in the pre-secretory period the epithelium and stroma of the plexus have the same potential. With the onset of secretion, however, the potential of the epithelium rises somewhat and the potential of the stroma falls markedly until there is a potential difference of 0.10 volt. This difference increases until in the last third of the gestation period it amounts to 0.23 volt.

In the secretory plexus, in addition to the difference of potential between epithelium and stroma it was also found that the basement membrane conducts electrons. The electric current so established between epithelium and stroma explains the selective transference of acid and basic dyes across the basement membrane. In the pre-secretory plexus, since there is no difference of potential between epithelium and stroma, there is no electric current and consequently no selective transference of dyes.

In explanation of the changes in potentials of epithelium and stroma, it is pointed out by Dr. Flexner that in the pre-secretory period indophenol oxidase is in low concentration and equally distributed between epithelium and stroma. As secretion begins this oxidase disappears from the stroma and is found in much higher concentration in the epithelium. Indophenol oxidase activates molecular oxygen for biological oxidations and in its presence, other factors being equal, the potential level of a tissue is raised. Thus these changes in potential seem to hinge on the distribution of indophenol oxidase.

In his studies of the biological processes underlying the formation of cerebrospinal fluid by the chorioid plexus, Dr. Flexner has made an analysis of the thermodynamics of ultrafiltration and has verified his theoretical deductions by experiments with sucrose solutions and to some extent with colloidal solutions. In this way he has obtained criteria for distinguishing whether the cerebrospinal fluid is a dialysate in equilibrium with the blood plasma, or an ultrafiltrate of the blood plasma, or a true secretion involving energy expenditure by living cells. In this work Dr. Flexner has found himself in the enviable position of the biologist who on reaching one of his frontiers is able to help himself out by making use of some of the pathways that have been developed in a neighboring discipline.

Chromosome Studies

Development of the Salivary Gland Chromosomes

Because of their unique interest an investigation has been made by Dr. J. B. Buck of the embryology of the giant chromosomes which are found in the larval salivary glands of Diptera. Using Sciara larvae he has traced the steps of transformation of these chromosomes from their original state, when in size and appearance they are like ordinary somatic chromosomes, until they attain their enormous size and typical banded appearance. In doing this he made measurements of the chromosomes, nuclei, cells, glands, and larvae in the living state. The finer morphology of the chromosomes was studied on fixed material for each stage of development.

It was found that the salivary gland attains its definitive number of cells soon after it arises in the embryo within the egg. Its subsequent growth is due entirely to increase in cell size and the greater part of this growth occurs in the late larval stages. What is true of the cell is also true of the nucleus and then in turn of the chromosomes, which compose 90 per cent of the nuclear volume. The nuclear volume doubles every 1% days during the period of the 4th to the 17th days, from which time to the beginning of pupation it becomes progressively less.

As to the structure of the chromosomes, it is found that in the early embryonic gland homologous chromosomes are paired, and are merely short slender threads. From the outset, however, each thread exhibits enlargements which correspond to those of its homologue. Each of the threads soon splits into two threads, retaining however some cross-connections. The homologues are thus doubled and shortly before the larva hatches from the egg these doubled homologues begin to twist or coil about each other and fusion between homologous regions begins. There is thus produced a fourstranded helically coiled flattened chromosome as early as 6% days after the egg is laid. Each synapsed pair of doubled homologues soon appears as a slender cylindrical and much elongated strand, showing diffuse crossbands at intervals which foreshadow the "banding" of the fully developed salivary chromosome. During the succeeding larval stages the chromosomes greatly increase in diameter, the banding becomes more pronounced, and the coiling reaches its maximum. Before pupation the coiling relaxes and the chromosomes become straighter, and this is the period of their greatest growth. As pupation sets in, however, these giant chromosomes begin to regress and finally during the pupal stage the larval salivary glands undergo histolytic degeneration.

In reference to the development of the banding, Dr. Buck found that the first ones to appear represent the heaviest bands of the definitive chromosome. They remain relatively unaltered during development, though they tend to darken and some of them separate into doublets. The new, light bands, which become visible as development proceeds, appear in the lengthening spaces between the heavier bands. They apparently do not split off from the latter.

This investigation is being carried further but already it has uncovered some very essential features which will need to be reckoned with by the chromosome cytologists and by the searchers for the gene.

Chromosome Puffing and Chromosome Knots

In his studies on the giant salivary gland chromosomes in Sciara Dr. C. W. Metz has turned his attention to the phenomenon of "puffing" and the structure of such regions. Instead of the characteristic banded structure the chromosome may vary in certain particular regions by becoming greatly expanded or "puffed." In such an area it is uniformly granular, resembling cytoplasm as seen in fixed preparations. It is evident that the segment involved has been increased in volume and that the increase is in the form of small achromatic droplets. Intermediate degrees of "puffing" show bands in various degrees of disintegration. Dr. Metz points out that the material in these "puffed" regions is perhaps comparable to that of the "chromocenter" in Drosophila, and if it is we must conclude that the "chromocenter" is not inert. From the study of living cells in tissue culture we have learned the wide range in form which cells may undergo with different physiological states, and our recent observations on chromosomes and their chromatin content tend to show that here, too, we have structures that are delicately responsive to the state of the nucleus and the circumstances of the environment.

In a former report reference was made to the evidence obtained by Dr. Metz of the presence of an insulating sheath surrounding the individual chromosome. In a review of the occurrence of chromosomal knots he adds further evidence of the existence of such a sheath. Simple knots are occasionally found midway in the giant salivary gland chromosomes of Sciara. It is evident that they arise early while the chromosomes are still small threads, but since the knots always involve both homologues they must have formed after the homologues had fused. The principal growth of the chromosome occurs after the completion of the knot, and this tends to make the knot a snug one. A knot can form only in the presence of free movement of the chromosome. At its initiation there must be a loop and the sliding of one part over another. That fusion does not result during the process is explained by Dr. Metz by hypothesizing an insulating sheath. As the chromosome becomes thicker and the knot becomes tighter it would appear on mechanical grounds that the segments involved would become deleted or, if the tenseness sufficiently overcame the protection of the sheath, fusion would follow and an inversion of segments would occur. Such events would explain some of the well-known genetic experiences.

Multiplication and Reduction of Chromosome Groups

Last year an account was given of the studies of Dr. C. A. Berger on the multiple chromosome complexes found in the larval ileum of the mosquito, where repeated division of the chromosomes occurs without division of the nucleus. That is, during the larval period the epithelial cells of the ileum grow by increase in cell size to three or four times their original volume without an increase in the number of cells. It is not until metamorphosis that division of the cells occurs. As metamorphosis progresses these cells repeatedly divide with corresponding decrease in their size and in the number of chromosomes until we come to the relatively small nuclei of the rebuilt imaginal ileum with its normal diploid number of 6 chromosomes. Here we have compounding of chromosomes which may well be compared to that seen in the giant salivary gland chromosomes. Since last year Dr. Berger's paper has been completed in its final form and has been published in volume 27 of the Contributions to Embryology.

Studies of the Pituitary Gland

Tissue Cultures of the Hypophysis

The study of the pituitary gland in tissue culture has been followed for several years by Mrs. M. R. Lewis. She found that such cultures taken from all the ordinary laboratory animals grow rapidly and abundantly, regardless of the age of the animal from which the gland is obtained. They grow particularly well in tube cultures. The cells retain their differentiation and continue to form their specific granules, though the granules are fewer than in the original tissue.

It was found that cells grown in cultures for as long as fifty days continued to produce blood-pressure-raising and melanophore-expanding hormones. In an effort to correlate cell types with specific hormones animals were sought in which cell types were so segregated that particular regions could be dissected out for transplantation. In the mouse the pars intermedia is free of pars nervosa tissue. In the chicken and armadillo the pars nervosa is free of other lobe tissue, whereas in the dogfish and skate the pituitary cells are segregated into six separate lobes. The melanophore hormone was located in two of these latter lobes and continued to form in cultures. Apparently tissue culture affords a valuable tool for determining specific functions of the pituitary cell groups, at least in the case of the hormones belonging to the posterior lobe. The hormones of the anterior lobe are more complicated in their activity and this has made them more difficult to identify. A review of the present status of her studies was given by Mrs. Lewis before the Association for Research in Nervous and Mental Disease.

Cytology of the Hypophysis

In a previous Year Book an account was given of the studies of Dr. I. Gersh on the relation of the histological structure of the posterior lobe of the hypophysis and the pressor, oxytocic, and antidiuretic hormones which are generally assumed to originate there. He was able to show that the hyaline bodies of Herring, which had been thought to be a secretion antecedent, are an artifact and are not present when the tissue is prepared under the best conditions. This left only neuroglia cells as the local source ; unless one concluded that these three hormones were made elsewhere and transported by the blood stream and deposited through means of a special capillary permeability and stored in the posterior lobe.

During the past year further study of the parenchymatous cells of the posterior lobe in rats has led Dr. Gersh to the conclusion that some of these cells are really glandular and that they produce and secrete the antidiuretic hormone. This posterior lobe glandular cell has been found by him in a wide variety of mammals and in pigeons and in chickens. It is characterized by the presence of either granules or lipoid droplets which can be seen in fresh mounts and which fill the cytoplasm and extend out into the cell processes. In the rat these droplets are rich in neutral unsaturated fats ; in some animals there are no visible lipoids. A characteristic feature of this glandular cell is that it appears early in embryonic life and that the number and size of the cells and of their inclusion bodies increase throughout life, reaching their greatest prominence in rats two and a half years old. Owing to the fact that there is a normal range in the number and size of these posterior lobe glandular cells in any particular gland, Dr. Gersh was able to show that fluctuations occur within this range which are correlated with the dietary intake of water. This fluctuation could be controlled experimentally. After rats have been restricted to a relatively dry diet for a week the glandular cells are present in greater number and are larger. On the other hand when the experimentally dehydrated rats are given free access to water, the number and size of the differentiated cells promptly revert to the normal range prevailing in untreated rats. Thus Dr. Gersh establishes a significant correlation of cellular activity and morphology with the hypersecretion of antidiuretic substances, and perhaps also of oxytocic substances.

It may be added that among the parenchymatous cells of the posterior lobe there are many that are relatively undifferentiated, but which during the hyperplasia, which follows the stimulus to hypersecretion, become transformed into the fully differentiated form. The differentiated and the relatively undifferentiated varieties vary inversely in number.


Nerve Terminations in the Posterior Lobe

Using pyridine silver preparations and fresh pituitaries of young rats perfused with methylene blue, Dr. C. McC. Brooks and Dr. I. Gersh have succeeded in demonstrating nerve fibers which pass down on the hypophyseal stalk to terminate in pericellular baskets around the glandular cells of the posterior lobe described in the preceding paragraphs. The endings almost completely enclosed the cells in a close-meshed network. The fibers belong to the hypothalmic hypophyseal tract. It was found that they are unaffected by the removal of the superior cervical ganglion, which would remove them from the category of the sympathetic chain, if that were necessary.

The demonstration of this nerve supply to the posterior lobe glandular cells gives us an explanation of the phenomena of pseudo-pregnancy, which had been recognized as requiring the transmission of nerve stimuli. It also becomes clear that section of the pituitary stalk would lead to degeneration of these terminations and an accompanying severe diabetes insipidus.

Reproductive System and Endocrinology

The Gilfillen-Gregg Skin Test for Pregnancy

A theory has been advanced that the abundant supply of prolan in the blood of pregnant women should render these individuals immune to further injections of urinary prolan, whereas the non-pregnant woman should be prolan-sensitive. Were this true it would constitute a simple and economical test for pregnancy. Two guest investigators in the laboratory, Dr. S. Saglik and Dr. E. Scipiades, Jr., have tested this technique on animals. After failing to obtain differential reactions in rats, guinea pigs, and rabbits, they made experimental injections of prolan in a series of monkeys, in a few of them in the form of antuitrin-S and in others in the form of follutein. Here, too, the results proved negative.

For purposes of control and as a test of the potency of the hormone used on the animals, skin tests were made with follutein in pregnant and nonpregnant women. Of 19 non-pregnant women only 11 gave the postulated reaction, whereas of 23 pregnant women, whose pregnancies varied between 16 and 40 weeks, 6 reacted in a manner expected only in non-pregnant women. It is thus clear that this test is not sufficiently reliable to replace the standard Aschheim-Zondek or Friedman test.

Time of Ovulation

In reporting observations on the formation of uterine epithelial plaques in the process of implantation of young monkey embryos, Dr. C. G. Hartman assembled and reported his records on ovulation. Among 300 ovulations accurately diagnosed, all occurred between days 8 and 16 with the exception of 5, which fell irregularly outside that period. This seems to be a mechanism whose precision is rarely surpassed among biological phenomena.

Alleged Birth of Triplets in the Macaque

Though multiple births may occur in the rhesus monkey it has been shown by Dr. C. G. Hartman that one must be on guard against being misled by a tendency to kidnaping that prevails among certain aggressive mother monkeys. In a case of apparent triplets it was possible for Dr. Hartman to show that two other recent mothers in the same cage had been deprived of their young, and also he obtained the conclusive evidence provided by the fact that the appropriative mother had but one recent corpus luteum.

The Anthropoid Ovary

The opportunity of studying the ovaries of three gorillas, two chimpanzees, one orang-utan, and one gibbon has been well utilized by Dr. S. Saglik, a guest of this laboratory from the Gynecological Clinic, Gulhane Hospital, Istanbul, in giving us an analytic description of the anthropoid ovary. He has also compared these ovaries with those of man and with those of the Old and New World monkeys.

Dr. Saglik finds that primate ovaries can be arranged in a series on the basis of their general similarity to the human ovary and he arranges them as follows: orang-utan, chimpanzee, gorilla, macaque, cebus, gibbon, Allouata, and Ateles. Here then we have another organ which would call for a very different phylogenetic tree from that demanded by the skeleton.

Menstruation

A study of the incidence of menstrual cycles without associated ovulation has been made by Dr. C. G. Hartman on 300 female monkeys of the Carnegie colony, concerning all of which he possessed fairly complete biological records. These animals with few exceptions were purchased from animal dealers and about one-third of them were superior specimens. Such animals ovulate either at once after arrival or at least after a few months' period of acclimatization. Another third of the animals received were inferior ones that either did not menstruate at all or menstruated without ovulation. The remaining third of the animals were intermediate in quality. They remained in excellent health but ovulated less reliably or in some instances never. This material provided Dr. Hartman with the opportunity of studying a very large number of cycles, a sufficient number to determine their principal variations. Of particular importance were his determinations of the frequency of nonovulatory cycles.

On analyzing the non-ovulating monkeys he found that the cycles could be separated into two groups, those in which the non-ovulatory cycles may be regarded as normal, and those in which the occurrence is pathological. His records include 1000 cycles in which non-ovulatory cycles occurred during the non-breeding season, from May to September. This appears to represent normal behavior. Also non-ovulatory cycles are normal in adolescence, of which there were 240 records. Likewise in the pre-climacterium and during recovery from pregnancy and lactation non-ovulatory cycles are normal. On the other hand, in 260 animals there were 1075 cycles in which there was no ovulation and which must be classed as abnormal or pathological. Some of these animals were palpably sick, and either did not menstruate at all or menstruated without ovulating a few times before death. About 30 per cent of the animals fell in this group. Then there are some apparently healthy animals which never ovulate or else only occasionally ovulate. Of the observed non-ovulatory cycles 17 per cent belong in each of these two groups. Some animals are unpredictable and ovulate about one-half the cycles of the breeding season. Such animals yielded a number of our finest embryos. Recently acquired animals are very likely to skip their ovulations for a time after their arrival. Some were with us two years before their ovulations started, some one year, and others began ovulating during the first year. Then among even the best animals there were some who occasionally failed to ovulate at the normal times. About 10 per cent of the nonovulatory cycles fell in this group. From these records it is seen that the non-ovulatory cycle is a very definite thing and becomes a factor that must be reckoned with in consideration of the occurrence of sterility.

Further studies have been made by Dr. Hartman on the hormonal control of menstruation. He has found that by periods of daily administration of testosterone in a monkey which has previously been regular in its menstrual cycles the cycle can be lengthened to 38 days as against 25 to 28 days previous to the experiment. In animals which have been castrated the bleeding which usually follows within a few days was inhibited by daily administration of testosterone. Also the menstrual bleeding which in favorable animals uniformly occurs following the injection of amniotin can be inhibited over prolonged periods. Thus Dr. Hartman shows that testosterone has an action upon menstrual control closely simulating that of progestin, just as it also simulates progestin in stimulating mammary development and in inhibiting the vaginal mucosa.

At this point reference should be made to the light thrown on the menstruation problem by the studies of Dr. J. E. Markee done in cooperation with Dr. Hartman. They made transplants of endometrium according to Dr. Markee's method and were able to follow the vascular changes by direct observation. This work is now in course of final preparation for publication. It will be reviewed in full in my next report.

Hormone Injections in Young Alligators

Before his appointment on the Johns Hopkins staff, Dr. T. R. Forbes had already, under Dr. R. K. Burns, Jr., made his experiments on the induction of a precocious development of the reproductive tract in the immature alligator by the administration of hypophyseal extracts. He had also studied the effects of female sex hormone injections (cestrone) in young alligators and found that it produced a marked hypertrophy of both ovarian and testicular cortex, along with greatly hypertrophied oviducts in the females and some development of the male vestigial mullerian ducts. This work has been published during the past year. Dr. Forbes has continued his hormone studies on the sexually immature alligator. He has investigated the effects of prolonged injections of testosterone in recently hatched animals and found them responsive to this hormone. In 14 females moderate hypertrophy of the oviducts took place, although the change in the ovaries was less definite. In the male the testes were twice as large as those of the control animals and there was definite hypertrophy of the vestigial mullerian ducts and of the penis. The wolffian ducts and the wolffian bodies were found unresponsive in both sexes to injections of these sex hormones. If we accept them as embryonic organs that perform an essential but temporary service for the embryo it removes them from the group of reproductive organs and would explain their failure to respond to either testosterone or cestrone.

Tissue Culture of Endocrine Organs for Purposes of Transplantation

Some tentative experiments have been made by Dr. G. 0. Gey toward obtaining pure strains of thyroid and parathyroid cells in continuous tissue culture from which homologous grafts can be made on individuals who through deficiencies of their own need these specific endocrine secretions. Thus far a number of successful grafts of thyroid cultures have been made in dogs and also a few parathyroid grafts. The advantage of tissue culture grafts is that in this way the desired endocrine cells can be acclimated to a tissue culture medium that is composed largely of the recipients' plasma and serum, thereby increasing the probability of their survival and functional activity.

Experiments on Castrated Animals

In recently castrated young male rats it has been found by Dr. J. Ball that the female hormone estrin, if given in daily injections of proper amounts (50 to 100 rat units), will definitely increase or completely restore their sex activity. The experiments were conducted on six male rats which were castrated at about four months old and the tests were begun two weeks later. Quantitative records were made both of their mating behavior and of their motor activity as registered by the revolving drum. The amount of hormone used was regulated by the response of the individual animal. After the castrate level of sex activity had been determined a sufficient amount of the hormone was given in daily injections to bring out an unquestionable response in each rat. From the results of these experiments Dr. Ball reached a conclusion that will be of interest to students of behavior, namely, that the function of this estrogenic hormone in the adult animal is not so much to organize the mating behavior pattern as it is to activate a pattern already laid down through other influences.

New observations have been made by Dr. C. G. Hartman on the results of castration in pregnant monkeys. Two animals castrated at the end of the third month of gestation carried their fetuses to full term. Three others castrated on the 46th, 35th, and 31st day, respectively, were progressing normally two months later. These results harmonize with the fact observed by Drs. Hartman, Corner, and Bartelmez that the corpus luteum of the rhesus monkey is active only during the first four weeks of pregnancy, at which time it markedly regresses. Theoretically its removal at any time thereafter should not interfere with the continuance of pregnancy and, as seen in these experiments, it does not.

Central Nervous System

Cerebrospinal Fluid

In his lectures given at the University College, London, Dr. L. H. Weed pointed out the importance to many fields of anatomical investigation of intimately combining anatomical and physiological thought, and paying equal regard to structure and to function. It was not necessary for Dr. Weed to point this out, since his own example in the study of the coverings of the brain and the specialized fluid that is contained within them had long since provided us with a brilliant demonstration of the advantage of blending these two disciplines.

The researches of Dr. Weed upon the cerebrospinal fluid now reach back 25 years. During that time he, along with a group of able coworkers, has unraveled an important series of fundamental problems regarding this intricate system, concerning which little was known when his investigations were starting. Under his guidance we have seen, as the readers of the Carnegie Year Books will know, the histology and embryology of the meninges clarified. This was followed by the demonstration of the sources of the cerebrospinal fluid and the pathways of its return to the venous system. There then followed the series of experiments which showed that the absorption of cerebrospinal fluid is the product of two factors, a hydrostatic one being the difference between the subarachnoid pressure and intracranial venous pressure, and the other the colloid osmotic pressure of the blood. This promptly led to the revelations regarding the pressure relationships between the cerebrospinal fluid and that in the cerebral veins, under the principle of the bony wall of the cranial cavity and the vertebral canal serving as a rigid container. There was then found the provision of elasticity which permits a dislocation of fluid on change in position by means of compensating dilatation and contraction of the intradural vascular bed, the cerebral venous pressure at the same time remaining constant. Associated with the latter experiments, a better hypothesis could be arrived at as to the primary function of the cerebrospinal fluid. It is owing to these researches of Dr. Weed that we now see it as a means of providing a prompt reciprocal volume and pressure adjustment when changes occur in the volume of the vascular bed or in the nervous tissue.

Effect of Inactivity on Nutrition and Growth of Muscle and Bone

The investigations of Dr. S. S. Tower on the isolation of the lumbar enlargement of the spinal cord in young growing animals has been extended to its trophic effect on the muscles and bones normally innervated from that source. In her experiments the cord was transected above and below the lumbo-sacral enlargement and all its posterior roots cut. When this is done the dependent muscles lose all ordinary activities including muscle tone. It was found that for purposes of these experiments young animals may survive several months and provide us with a method of studying the regressive changes which follow nerve section. Also in such experiments one can discriminate between effects of inactivation and those of nerve degeneration.

The three puppies used by Dr. Tower were studied 2, 5, and 6 months respectively. By the nature of her experiment all ingoing nerve impulses were excluded from the isolated cord, which nevertheless survived along with its dorsal root ganglia and peripheral nerves, without developing within itself any nervous activity. Since Dr. Tower had previously shown that severing of the posterior roots is without appreciable trophic influence on skeletal muscle, any trophic disturbances resulting from these experiments would therefore have to be ascribed to the inactivation.

It was found that atrophy and metaplasia of muscle tissue into fibrous tissue, atrophy and destruction of subsarcolemmal nuclei, and interstitial fibrosis are all characteristic of inactivation of skeletal muscle. Macroscopically such muscles can be seen to be atrophied and they develop contractures. Microscopically the fibers are smaller in all dimensions, pale staining, and in the process of transformation into fibrous tissue, and the interstitial fibrous tissue is increased. The innervation remains largely intact.

All these things occur also in denervated muscle. But when a muscle is denervated it shows a rapid proliferation and change in character of the subsarcolemmal nuclei, which changes do not follow inactivation alone. This specific nuclear proliferation must be attributed to the degeneration of nervous tissue. Dr. Tower thus finds that the trophic control of muscle by the nervous system requires both physical integrity of innervation and nervous activation.

In analyzing the effects of inactivation on the postnatal growth of bone it was found that the long bones of the leg were normal in length and in their general configuration, features which appear to be intrinsic. In thickness and certain details, such as elevations at muscle attachments, they were underdeveloped. These then depend on extrinsic factors which in the above experiments were abnormal because of the presence of muscle inactivity. Special trophic nerves continue to be unnecessary to Dr. Tower for the discussion of the nature of trophic control of tissues.

Electrophysiology of Nerves

It is only recently that any of our group have participated in investigations on the electrical properties of functioning nerve fibers. During the past year Dr. H. A. Howe in cooperation with Dr. D. A. Clark has made observations on fiber action potentials in the fiber tracts located entirely within the central nervous system. Observations on fiber action potentials had previously been restricted to peripheral nerves.

Dr. Howe and Dr. Clark studied the changes produced in the electrical potentials of the tracts within the cervical spinal cord following induction coil stimulation of the pyramidal tracts which lie on the ventral surface of the medulla oblongata, in the cat. They were able to demonstrate potentials somewhat analogous to those characteristic of peripheral nerves. The responses, however, were very complex and evidently included the activity of many fiber pathways. Owing to the structure of the cord it was not possible to determine the correlation between conduction velocity and threshold as has been done with peripheral nerves. Under the conditions of their experiments they obtained potentials which in form, rate of conduction, and resistance to asphyxia gave the picture of neuronic fiber activity without synaptic intervention.

These investigators applied their stimuli to the pyramidal tracts by means of a bipolar electrode having two silver contacts set flush in the end of a bakelite rod. This rod was inserted tightly into a trephine hole through the base of the skull, in a manner that avoided blood loss or leakage of cerebrospinal fluid. The resultant disturbances were registered by coaxial needle electrodes inserted into the cord at different distances from the point of stimulation. The two levels chosen were an upper one at the level of the second cervical vertebra and a lower one at the level of the fifth cervical vertebra.

Dr. S. S. Tower participated in a study of impulses as they pass through a sympathetic ganglion and into the nerves beyond it. She had the privilege of working with Dr. D. W. Bronk and his associates, who are experienced investigators in the field of electrophysiology of nerves. Their experiments consisted in stimulating the preganglionic fibers, rami to the stellate ganglion from the spinal cord, and recording the action potentials in the relatively long inferior cardiac nerve, to which the impulses were transmitted through the ganglion.

It was found that the conduction velocities in the nerve studied had a considerable range (1.4 to 0.6 meters per second), and there is a considerable temporal diversity in the maximum potential. Following the peak there is a positive after-potential which may be increased during the course of a tetanus. Likewise a negative after-potential develops after a tetanus. A rested nerve does not generally show a negative after-potential.

The significance of the action potential records which are yielded by the oscillograph is not altogether clear, and it is necessary at present to study them in all their details and under all possible experimental conditions. Among other things it was found by these investigators that a rapid series of preganglionic impulses initiates a single but dispersed series of postganglionic impulses. The records show that the individual nerve cell discharges but one impulse for each series. The dispersion appears to be due to differences in conduction time for the various fiber pathways through the ganglion. It was also found that the number of ganglion cells that respond to a preganglionic stimulus may be modified by various things. Arrest in the blood circulation decreases the number, whereas repeated stimuli can build up a larger response even in a non-circulated ganglion. Perfusion of a ganglion with drugs also modifies the nature of the responses. Although some of the terminology, the technique, and the character of the records are somewhat confusing to one who is not oriented in such matters, it is to be remembered that the workers in this field are collecting observations that lead to something more tangible as to the nature of the conduction of nerve impulses than the pure speculations which formerly were our sole resort. Some of the ground work in the electrophysiology of protoplasm was done with Valonia, that interesting primitive organism which abounds in the waters at the Tortugas Laboratory.

Regeneration of the Facial Nerve and Associated Tics

In Year Book No. 35 a brief account was given of branched axones of the facial nerve in monkeys following experimental injury of that nerve. The results of those experiments have been published during the past year in final form in the Archives of Neurology and Psychiatry under the authorship of Dr. Howe, Dr. Tower, and the late Dr. A. B. Duel, who were aided by a grant from the Carnegie Corporation. These investigators have established, both physiologically and anatomically, the fact that in regeneration of the facial nerve, following injury, its axones at that site undergo branching and subsequently innervate widely separate muscles and that in this way an irrevocable functional union takes place between muscles which do not normally contract simultaneously. There thus occurs a condition which resembles the tics which in humans follow injury of this nerve, and is characterized by an indiscriminate mass contraction whose proportion varies as the amount of damage to the nerve. These contractions show no tendency to regress, even over a three-year period. In man there is a better expectation of being able to suppress or modify the tic movements through reeducation.

Imitative Behavior in a Monkey

A case of what appears to be imitative behavior in a young rhesus monkey has been studied by Dr. J. Ball. Being caged with a kitten for company, this 11-month-old animal learned to drink liquids by lapping, copying perfectly the technique of its companion. The new method of drinking continued several months, as long as the animal lived. The normal way of drinking and the one originally employed by this animal is a process of sucking. Among 600 rhesus monkeys whose habits have been closely followed in this laboratory, none have ever been observed to drink by lapping in this open-mouthed fashion. Dr. Ball concludes that this case can be interpreted as imitation.

Brain of the Whale

Another contribution to the structure of the brain of the whale has been made by Dr. 0. R. Langworthy in collaboration with Dr. F. A. Ries. Because of its many interesting adaptations to the requirements of marine life, Dr. Langworthy has made the whale brain the subject of several investigations, as the reader of these reports will know. The present investigation includes eight additional brains of the sperm whale, Physeter catodon, making Dr. Langworthy 's collection, now housed in the Department of Neurology of the Johns Hopkins University, particularly adequate for such study.

Defective Brain Development

Dr. P. A. Fitz-Gerald of the Department of Anatomy, University College, Dublin, while a guest of our laboratory during the past year has made a study of the cerebral hemispheres of an eighth month child showing defective brain functioning. In the central and parietal regions the cortex of this child, instead of being properly fissured, was found to be almost smooth, and symmetrically so on the two sides. All the other cortical areas appeared to be normal. Dr. Fitz-Gerald associates the stunting of sulcus formation with a developmental arrest in cortical histogenesis and in this way he is helping to solve the problem which has long confronted the embryologist, of what is the exact nature of the forces that produce fissures and convolutions on the brain surface. He is following his surface survey of the material with a microscopic study of the tissues involved.

Morphological Studies

Clavicles and Long Bones of the Limbs in Man and Apes

In order to obtain suitable data bearing upon variability and asymmetries in higher primates and their comparison with man, Dr. A. H. Schultz has collected measurements and observations on a total of 753 human skeletons belonging to a variety of races, and a total of 530 simian skeletons belonging to all the genera of anthropoid apes and to macaques. The data have been obtained with the same technique and for the most part by himself and with the primary intention of its use for the study of variability and asymmetry. With it he has been able to make comparisons between some civilized and uncivilized races of man and comparisons between man and other primates, particularly the anthropoid apes. Heretofore we have had infinitely more data on asymmetries and variation in man than in other animals. Dr. Schultz has now provided the information regarding other related forms which we needed for evaluation of the data which were already available for man.

Among his observations on asymmetries he found, in comparing their distribution in man with that in apes and the macaque, that in general symmetry is rarer in the former than in the latter and that preference of asymmetries for one side is not nearly as marked in the apes as it is in man. In the macaque asymmetries favor both sides with practically the same frequency. In regard to asymmetries of the lower extremities man does not differ essentially from the other primates. In all primates there is comparatively little preference of one lower extremity over the other. Asymmetries in the lengths of the clavicles favor both sides with practically equal frequency in gorilla and chimpanzee and the right side slightly more frequently than the left in orang-utan, gibbon, and the macaque. This contrasts strikingly with the conditions in man, in whom there is a definite tendency for the left clavicles to be longer. In all the human groups the lengths of the long bones of the arm favor the right side in the great majority of cases, and the asymmetries of the arms favoring the right side are more frequent in females than in males among whites, Negroes, Eskimos, and Indians. Since Dr. Schultz had previously shown a similar prevalence of asymmetries in human fetuses, he concludes that the common preferential use of the right arm in man cannot be held responsible for its definite tendency to be longer. Nor is it likely connected with "right-handedness" since "left-handedness" is much rarer in man than are asymmetries favoring the left arms. Furthermore "lefthandedness" is regarded as hereditary, whereas asymmetries of the human body are thought not to be.

In general the tables of Dr. Schultz demonstrate conclusively that man differs strikingly from apes and monkeys in regard to both the percentage distribution and the relative amount of asymmetries of the clavicles and the long bones of the arms ; and that man and other primates are practically alike in regard to the degree of asymmetries and the difference in the preference of asymmetries for the two sides in the long bones of the legs.

Vertebrae and Length of Spinal Regions in Primates

From observations made on 300 freshly killed catarrhine primates, with measurements made from the centers of the intervertebral disks, Dr. Schultz has been able to show that the cervical and the thoracic vertebrae are proportionately larger in all higher primates than in the lower catarrhines, and that among all primates man has the relatively longest cervical and thoracic regions and the comparatively largest lumbar vertebrae. However, the common evolutionary trend among higher primates to reduce the number of vertebrae and the relative length of the lumbar and caudal regions has gone to greater extremes in some anthropoid apes than in man.

In a series of 80 adult gibbons, having a much greater vertebral variability than man, it was found that a reduction in the number of thoraco-lumbar vertebrae is not accompanied by a corresponding reduction in the relative length of this region. On the other hand, a close correlation exists between decreased numbers of thoraco-lumbar vertebrae and increased numbers of sacral vertebrae. Less frequently the sacrum increases its number of vertebrae at the expense of the coccygeal region.

As compared with the lower catarrhines, man and the anthropoid apes differ not only in possessing fewer thoraco-lumbar and caudal vertebrae and more sacral vertebrae but also in having comparatively longer cervical, thoracic, and sacral regions and much shorter lumbar regions.

Shoulder Architecture

In previous reports reference has been made to the studies of Mr. Brazier Howell on the architecture of the shoulder in the vertebrate classes, including Amphibia and Reptilia. To these may now be added studies on the shoulder region of birds and therian Mammalia. In his description of the domestic fowl Mr. Howell has made a contribution to comparative anatomy by the interpretation of the avian shoulder in terms of the tetrapod animal. As in his other studies, due emphasis has been given to innervation in all questions of muscular homologies.

Among the noteworthy details pointed out by Mr. Howell are the following: the spinal accessory nerve and its associated muscles are absent, being replaced by a suboccipital group; m. levator scapulae is lacking; the rhomboids occur in two layers; the subscapularis is poorly represented, whereas the dorsalis scapulae and deltoid are robust; the large breast muscle represents the pectoralis minor element, the major being small and deep; supraand infraspinati are absent; and the brachialis is a feeble muscle near the elbow.

In the anatomy of the appendages Mr. Howell finds a large break between those of the therian mammals and those of reptiles and even those of prototherians. In fact he finds that the monotremes are more comparable with reptiles than they are with therian mammals. For that reason he omits them from his analysis of the mammalian shoulder. He accounts for the great dissimilarity in the pectoral appendages of the above groups by the differences in the way the limbs are used. He points out the prone position of the reptilian body and the horizontal position of the humerus, with divergent elbows, features which call for a very different skeletal and muscular provision from that with which we are familiar in mammals. The reptilian type of shoulder architecture is quite unsuited for quick movements and longsustained action. In order to change the reptilian into the mammalian plan it was only necessary for reptiles to bring the elbow beneath the body. But this required such complicated skeletal and muscular adjustments about the shoulder joint that only a single reptilian group (Theriodontia) ever succeeded in its accomplishment. The improvement in function which resulted from the invention of the mammalian plan of shoulder seems to have played a large part in the development of the class Mammalia. The new deal provided the mammals with a means of using their limbs in a single plane, for purposes of locomotion, and over extended periods with the expenditure of much less energy. Over and above his interesting interpretations Mr. Howell's study has brought together a large amount of information regarding the shoulder region of mammals that will be of much value to the comparative anatomist.

Muscles of Hip and Thigh

The comparative anatomical studies which Mr. Brazier Howell has been making on the shoulder girdle have been supplemented by a similar method of analysis of architecture of the hip and thigh. His material includes the domestic fowl, the giant Japanese salamander, the reptile Iguana, and many varieties of mammals, a sufficient material for a comprehensive review of the homologies of the pelvic girdle.

It is pointed out by Mr. Howell that though the pelvic and pectoral girdles show many resemblances, yet the structures of neither pair can be properly homologized with those of the other, because of their difference in derivation. The cartilaginous pectoral girdle developed as an adjunct of the membranous girdle and is really a part of the head and axial skeleton. When the limbs became the primary organs of locomotion it was the pectoral limbs that propelled the animal by traction, and the girdle movement accompanying this action was accomplished largely by sidewise movements of the head. The membranous part of the girdle was derived from the posterior margin of the gill basket, whose musculature (trapezius) contributed to the control of the girdle. It had the complication of having a dual origin (membranous and cartilaginous) added to the fact of its location at the anterior termination of the axial musculature. With the pelvic girdle matters were quite different. The latter was initiated without the influence of anchorage to the axial skeleton, inasmuch as the pelvic appendages at first functioned for support only and not propulsion. For a long time they remained free of the axial skeleton, that is, from the viewpoint of the phylogenist. Furthermore the influence of the body muscles upon the pelvis were quite different from that upon the shoulder girdle. The story of the difference in functioning of the pectoral and pelvic limbs in the progress of their assumption of more complicated functions has been worked out in its significant details and Mr. Howell has provided the anatomist with a rationale for this region which is a definite advance over that heretofore available. With his four-group basis as the chief criterion, he has been able in large part to homologize the pelvic muscles of urodeles, lacertilians, mammals, and birds. Even so there remain some specializations which still obscure their precise relationships.

Visceral Anatomy of an Infant Chimpanzee

An infant female chimpanzee, 74 days old, which died of an acute pulmonary infection, provided Dr. W. L. Straus, Jr., with an opportunity to study the thoracic and abdominal regions at this early stage. The body was injected with a 10 per cent formalin solution within one-half hour following death, giving excellent preservation of the tissues. Anatomical data on the viscera of this important primate are relatively scant and this appears to be the youngest infant thus far systematically studied. The sitting height and trunk height, measured after fixation, were 31.5 cm. and 16.8 cm., respectively. On comparing this specimen with an older chimpanzee and with an infant orang-utan Dr. Straus found that there are but small differences in visceral morphology between the two chimpanzee specimens though there is a difference of nearly four years in their age, whereas the contrasts between the infant chimpanzee and infant orang-utan are many and striking, an observation that will not surprise those who are genetically minded. Dr. Straus has made his detailed descriptions and measurements available to other investigators by formal publication.

Branches of the Aortic Arch in the Monkey

In Year Book No. 35 the investigations of Dr. C. F. De Garis on variations in the branches of the aortic arch in the macaque monkey were referred to and at that time the value of having a large number of specimens from a single species was pointed out. To his first series of 115 specimens, he has now been able to add 153 more. This provides a total series large enough for significant statistical treatment and for the consideration of problems of variation, inheritance, and symmetry. The new material when arranged in polygons of frequency further substantiates a norm having a short truncus communis comparable to that often found in man. This norm has a marked modal value which is intermediate between human and mammalian patterns, with almost equal distribution of these patterns on either side of the norm. The next step appears to be the search for correlations of this norm with trunk measurements and visceral structure and the consideration of the influences of body symmetry. This will inevitably lead the investigator back into the fetal period, where a large part of the determination of the vascular pattern takes place.

Asiatic Primate Expedition

Joining forces with Professor H. J. Coolidge of Harvard University and Dr. R. C. Carpenter of Columbia University, Dr. A. H. Schultz participated in an expedition to northern Siam and British North Borneo in search of anthropoid material that is native there, and particularly the gibbon and orang-utan. Their program included comprehensive observations on the behavior and social relations of entire ape families as they live in their native jungles, and on the other hand the collection of skins, skeletons, embryos, parasites, stomach contents, bodily measurements of the dead animals with a view toward species characters, growth before and after birth, variability, incidence of disease and injury, and any facts relating to pregnancy. Through careful preparations for the expedition and through the interest and assistance of the authorities of the countries which they visited they were able to obtain data and specimens for subsequent study at their home laboratories, in amount far beyond their expectations. From his own standpoint the large collection of gibbon specimens that has thus become available more than justifies the time and effort that Dr. Schultz devoted to the undertaking. The skeletons are now being cleaned and prepared for study.

Physiological Observations on Fireflies

As a collateral to his cytological studies on insects Dr. J. B. Buck published during the past year his records on fireflies, an extensive collection of which were obtained by him on a visit to Jamaica in the preceding year while a fellow in the Zoological Laboratory of the Johns Hopkins University. In general he found that each species is rather definitely confined to a particular altitudinal range. A few species were found in a single district but most species are found in multiple regions where the altitude determines the appropriate temperature and moisture.

The observations by Dr. Buck on the spectral composition of the light emitted by the fireflies are of especial interest. Under the spectroscope the light emitted by all the species investigated produces a broad structureless band lying wholly within the visible spectrum. In no case was the light below 5050 or above 6550 Angstrom units. It is found that several species emit light of the same spectral composition, whereas others differ from one another. It is also noted that the spectra of some species present a relatively extensive range, e.g. 5050 to 6450 Angstrom units. Finally, Dr. Buck was able to demonstrate photographically that the apparently different color of the light emitted by the thoracic and abdominal light organs in certain species is due to an actual difference in the color and is not a subjective effect.



Cite this page: Hill, M.A. (2019, May 25) Embryology Report - Carnegie Year Book 37. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Report_-_Carnegie_Year_Book_37

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