The Development of the Adrenal Gland of the Cat.

Transcription

1 The Development of the Adrenal Gland of the Cat. By Sarah Davies, M.Sc, University of Liverpool. With Plate 13. CONTENTS. PAGE I. INTRODUCTION. 81 II. MATERIAL III. TECHNIQUE IV. THE ADRENAL GLAND OP THE CAT AT DIFFERENT STAGES OF DEVELOPMENT. 87 A. Foetal GlandB. 87 B. Sub-adult Glands. 92 V. GENERAL DISCUSSION AND SUMMARY. 97 I. INTRODUCTION. THIS paper deals "with the development of the adrenal gland of the cat. A search of the literature has revealed that very little work has been done on this subject. In 1908 Soulie described the development of the adrenal gland of the cat during foetal life. He states that the first appearance of the adrenal is seen in a foetus measuring between 6 and 7 mm. in length, where it is represented by small centres of cell proliferation in the coelomic epithelium. At the 12 mm. stage it is represented by a homogeneous mass of cells adhering to the wall of the inferior vena cava. In a foetus of 16 mm. the cells of this mass have assumed a reticular arrangement. Between the 16 mm. and 18 mm. stages the rudiment (anlage) of the gland is invaded by parasympathetic elements derived from near-by sympathetic abdominal ganglia. These parasympathetic elements continue to penetrate the gland until the 4 cm. stage, after which very little further invasion is seen. The parasympathetic cells pass to the centre of the gland and give rise NO. 317 G

2 82 SARAH DAVIBS to the medulla, whilst the original rudiment forms the cortex of the gland. He says that in a foetus of 9 cm. the cortex is fully differentiated into an outer zona glomerulosa, a middle zona fasciculata, and an inner zona reticularis. He further states that at birth the gland has practically assumed the adult structure, although there is still a slight intermingling of cortical and medullary tissue at the junction of the two regions. The zona fasciculata is said to be very narrow at this stage while the zona reticularis, on the other hand, is very extensive. This latter observation is interesting in the light of subsequent investigations described below. A considerable amount of work has been done on the development of the adrenal in other mammals. In 1911 Elliott and Armour recorded that in the early human foetus the adrenal cortex consists of an outer narrow zone of small cells and an inner highly vascular mass of cells free from fatty substances and forming the greater part of the foetal cortex. At this stage the medulla is said to be represented by small groups of cells scattered here and there throughout the inner mass. The large size of the human suprarenal gland during foetal life is stated to be due to a marked hypertrophy of the inner cortical mass, which begins at a very early stage and continues until birth. At full term the medulla is said to be entirely central. Immediately after birth the inner cortical mass begins to degenerate and has completely disappeared by the end of the first year. Meanwhile, at the end of the seventh month, the cells of the outer narrow zone assume the appearance and arrangement of the cells of the adult cortex 1 and store up fatty substances. These cells alone develop into the adult cortex. In 1912 Glynn recorded that the human adrenal during foetal hfe is at first larger than the kidney, this large size being due to a hypertrophy of the inner portion of the foetal cortex. This begins to degenerate immediately after birth, and the adult cortex is developed from an outer rim of small cells. In 1919 Jackson recorded that in the newly born albino rat 1 Elliott and Armour give no details in regard to the different layers of the cortex.

3 ADBENAL OP THE CAT 83 the zona glomerulosa, zona fasciculata, and zona reticularis are all present in the cortex, lipoids being uniformly distributed throughout all three zones. He states that at birth cortex and medulla are not distinctly separated, there being a certain amount of intermingling of cells at the junction of the two regions. He further states that during the confluence of the medulla in the first week after birth the cortical cell-strands within it are absorbed, and that during further growth the cortex increases rapidly, the medulla but slowly. In 1922 Weymann recorded that in the pig embryo the medulla is formed by cell groups, derived from the sympathetic ganglia, penetrating the cortical anlage and accumulating in the centre of the gland. The first really detailed account of the intra-uterine development of any adrenal was given in 1925 by Cooper, who worked on the human foetus. According to Cooper's description, in a foetus of 8 weeks the gland consists of an outer narrow zone surrounding a central mass. The outer zone consists of small cells with vacuolate cytoplasm and deeply staining nuclei. The central mass consists of large, angular cells loosely arranged and separated by intercellular spaces occupied by capillaries. These cells are granular and possess large nuclei with deeply staining nueleoli and nuclear membrane. (At 3 months these cells are described as eosinophil.) ' The peripheral cells are epithelial in origin and form the cortical anlage of the developing suprarenal gland, while the central cells, derived from the cortical anlage, constitute the boundary zone' (loc. cit., p. 34). No further details are given of the origin of the boundary zone. At a later stage, during the third month of intra-uterine life, the gland still consists of an outer narrow zone surrounding a central mass. The outer zone still consists of small cells with deeply staining nuclei and vacuolate cytoplasm, and the central mass consists of large cells lying end to end in a reticular manner and enclosing capillary spaces. These cells present an almost syncytial appearance, their boundaries being difficult to distinguish. Their cytoplasm is granular, and they possess large pale nuclei, with deeply staining nueleoli. 'The narrow zone of small deeply stained cells at the periphery of the adrenal body is the true

4 84 SARAH DA VIES cortex. The large central mass is the boundary zone and is also part of the foetal cortex' (loc. cit., p. 36). At the junction of cortex and boundary zone, however, lying free in the spaces between the cells of the latter, are small masses of cells with intensely vacuolate cytoplasm and very deeply staining nuclei. According to Cooper these are ectodermal sympatho-chromaffin cells which have made their way into the adrenal gland from accumulations of such cells situated between the adrenal bodies and the kidneys. These accumulations represent the future abdominal sympathetic ganglia. As development proceeds the outer zone or true cortex continues to increase in size, its cells becoming more vacuolated and arranged in columns like those of the fasciculate layer of the adult cortex. The boundary zone diminishes in size, while the number of sympatho-chromaffin cells increases, and they become more concentrated in the centre of the gland. At mid-term most of these cells are in the centre of the gland, but a few are still scattered in the boundary zone. After mid-term all have reached the centre of the gland. During the eighth month, and at the conclusion of intra-uterine life, the cortex is wide and is differentiated into two zones, an outer narrow zona glomerulosa, immediately within the capsule surrounding the gland, and an inner wide zona fasciculata. The cells of both zones are vacuolate, those of the zona glomerulosa being arranged in small groups and those of the fasciculate zone in columns. ' The inner ends of the columns are penetrating into the boundary zone and forming the zona reticularis' (loc. cit., p. 39). The boundary zone has diminished in size and the centre of the gland is occupied by masses of sympatho-chromaffin cells, many of which are developing into medullary cells with granular cytoplasm, whilst others are developing into sympathetic ganglion cells. The latter, however, were not found in all cases. At this stage there is no true medulla. During early post-natal development the cortex increases in size, the boundary zone gradually disappears, and the medulla becomes fully denned, consisting of loosely arranged cells with granular cytoplasm and large pale nuclei. With the complete disappearance of the boundary zone at about 18 months the cortex comes into direct contact with the medulla. At this stage

5 ADRENAL OF THE CAT 85 the zona reticularis is still ill denned. At 3 years, when the gland assumes the structure characteristic of the adult, the zona reticularis is well marked and consists of 'large, finely vacuolated cells in reticular arrangement, enclosing large blood spaces in the meshes' (loc. cit., p. 42). Since my own research on the adrenal of the cat, herein recorded, another worker in this department has investigated the development of the mouse adrenal in great detail (Waring, 1935). He has shown that in the mouse the cortical anlage arises at about the twelfth day of foetal life from the mesenchyme. During the fourteenth day this cortical mass is invaded by sympatho-chromaffin cells which gradually migrate to the centre of the gland and form the medulla. The outer region of the cortical anlage gradually becomes differentiated to form the adult cortex, the glomerular, fasciculate, and reticular layers appearing in order from the periphery inwards, but there is no previous distinction between an outer zone and an inner mass such as is reported for the human gland. A large part of the original cortical mass, in the mouse, takes no part in the formation of the adult cortex and remains as a broad zone of relatively undifferentiated tissue lying between the cortex and the medulla, and interlocking with the medulla. This 'interlocking zone' remains till about the thirtieth day after birth in the male, until a considerably later period in the virgin female, or until the first pregnancy. Waring points out that this interlocking zone is probably homologous with the boundary zone of man, but that the homology is not certain because the origin of the boundary zone is not known. Thus, according to Soulie (1903), Weymann (1922), Cooper (1925), and Waring (1935), the medulla is described as arising from cells of sympathetic origin, the sympatho-chromaffin cells, which invade the cortical anlage and accumulate in the centre of the gland. According to all investigators of the human adrenal Elliott and Armour (1911), Glynn (1912), and Cooper (1925) the foetal cortex consists of an inner and outer portion, the latter alone giving rise to the adult cortex, while the inner part degenerates during development. According to Waring in the mouse also the whole adult cortex arises by differentiation

6 86 SAEAH DA VIES of the outer part only of the foetal cortex, the inner part degenerating though not till adult life. According to Soulie (1903), however, in the cat this inner portion of the foetal cortex becomes the reticular zone of the adult cortex. My own investigation has shown that, contrary to the statement of Soulie (1903), the development of the adrenal gland in the cat shows the same sequence of events as that described in man. II. MATEEIAL. The material used for the present investigation came to hand incidentally in the course of a study of variations in the adrenal gland of the cat. As the material was not collected systematically for the present research, it is in many respects very limited. For the purpose of the larger investigation 111 animals were dissected. Of these 18 were sub-adults and 18 were pregnant females. As all the animals were obtained from the general population, neither age nor stage of pregnancy was known. In the case of the pregnant females the foetuses were removed and measured laterally 1 from the crown of the head to the anus, these measurements being taken as a very rough indication of the stages of development. Naturally, such measurements are not a reliable indication of the exact age of the embryos. The difficulty of measuring makes the margin of error comparatively large; also the individual variation in size of the foetuses from one animal is considerable, and it is almost certain that the variation in foetuses of the same age from different animals is even greater. Nevertheless, the lengths of the foetuses do give some indication of their stage of development. All the foetuses were removed from every pregnant female obtained, but in most cases it has only been possible to examine the glands of one foetus from each litter. In one instance every member of a litter of five (48 hours post-natal) was examined, 1 The foetuses were measured laterally owing to a misunderstanding. Foetuses are usually measured along the mid-dorsal line from the crown of the head to the root of the tail. My measurements, therefore, though perfectly valid for comparison with each other, are not comparable with those of other workers.

7 ADRENAL OP THE CAT 87 and all the adrenals were found to be at the same stage of development. The sub-adults were weighed in order to obtain some indication of their age. Clearly such weights are no real criterion they serve only to separate the very young from those distinctly older. Consequently, their glands, as described below, are not necessarily arranged in exact order of age; but the general order of adrenal development is clear. III. TECHNIQUE. All the cats were chloroformed, and in every case both glands were removed while the body was still warm. All adherent extraneous tissue was dissected away and one gland of each pailwas fixed in Bouin's fluid, the other in Zenker's fluid modified after Helly, the former proving the more suitable for histological work. The glands were sectioned at a thickness of 6/x and stained in Ehrlich's haematoxylin and eosin. IV. THE ADRENAL GLAND OF THE CAT AT DIFFERENT STAGES OP DEVELOPMENT. Descriptions are given below of the adrenals of eighteen foetal and eighteen sub-adult glands. A. Foetal Glands. The glands are described in what appears to be the order of their adrenal development. Stage No. 1. (See fig. 1, PL 13.) (Two foetuses, from different mothers, were examined at this stage of adrenal development, each measuring 3 cm. in length.) A transverse section of the glands of these foetuses showed a central mass of cells surrounded by a single narrow outer zone. This outer zone consisted of compactly arranged small cells with pale granular cytoplasm and pale, well-defined nuclei, the nucleoli and nuclear membrane alone being deeply stained. Scattered among these cells could be seen a few large cells with vacuolate cytoplasm and small, black, circular nuclei. The central mass occupied practically the whole of the gland and

8 88 SARAH DA VIES consisted of large cells loosely arranged in a reticular manner. The boundaries of these cells were difficult to distinguish. Their cytoplasm was densely granular and strongly eosinophil, and their nuclei were large and well defined, the nucleoplasm being pale in marked contrast to the deeply staining nucleoli and nuclear membrane. At the periphery of the central mass a few of the large vacuolate cells with small black nuclei were seen lying freely among the granular cells, but they were entirely absent from the more central regions of the gland. Stage No. 2. (Three foetuses were examined, all from different mothers. Two measured 5 cm. in length and one measured 5-5 cm.) This stage presented the same general appearance as Stage 1, but the cytoplasm of the cells of the peripheral zone was slightly vacuolate. Also the large vacuolate cells with small deeply stained nuclei were more numerous in the periphery of the central mass than in Stage 1 described above, and many such cells could now be seen also in the centre of the gland whither the other cells of this type appeared to be migrating. Stage No. 3. (See fig. 2, PI. 13.) (One foetus was examined ; length 7 cm.) The general appearance was somewhat the same as in Stage 2, but the cells of the central mass, where it abutted on to the outer zone, tended to be more compactly arranged than those nearer to the centre of the gland. Both the peripheral narrow zone and the outer region of the central mass were comparatively free from the vacuolate cells which were now more concentrated in the centre. Apparently the process of immigration, the beginning of which was seen in the glands previously described, is here more advanced. Stage No. 4. (One foetus was examined; length 8 cm.) The cells of the narrow zone at the periphery of the gland here tended to be arranged in small groups, separated by connective tissue continuous with the outer capsule. Internal to this zone was a wider zone of large, compactly arranged, deeply granular cells evidently belonging to the original central mass,

9 ADKENAL OP THE CAT 89 the remainder of which formed a loose reticulum in the centre. The large, intensely vacuolate cells with small black nuclei were but sparsely scattered throughout the peripheral zone and compact outer region of the central mass, and were more concentrated in the reticular portion occupying the centre of the gland. Stage No. 5. (One foetus of this stage was examined and measured 9 cm. in length.) The gland presented very much the same picture as that of Stage 4, but now the large, intensely vacuolate cells occupied the greater part of the centre and were almost confined to that region. Some strands of the original central mass were still present in the central region. Stage No. 6. (One foetus was examined; length 9 cm.) The peripheral zone now showed an increase in width as compared with previous stages. The vacuolate type of cell was even more predominant in the centre of this gland than hitherto, the densely granular, deeply staining cells of the original central mass tending to be relegated to a zone lying immediately within the original peripheral zone. In some sections a large group of a totally different type of cell was visible at the periphery of the central mass adjacent to the outermost zone. These cells possessed granular cytoplasm, in which they resembled the granular type of cell of the central region, but their nuclei were similar to those of the vacuolate type of cell, being small, circular, and deeply stained. These cells were not found in any other gland and they are not at present understood. Stage No. 7. (One foetus examined; length 10 cm.) The general appearance was very similar to that of the preceding stage. The deeply staining cells of the inner wide zone were more compactly arranged where they abutted on to the outer zone, but towards the centre of the gland were still loosely arranged in a reticular manner. The groups of large vacuolate cells in the centre were lying freely in the interspaces of the reticulum.

10 90 SAEAH DA VIES Stage No. 8. (One foetus was examined; length 10 cm.) The accumulation of the vacuolate type of cells in the centre of the gland was even more marked than previously. Stage No. 9. (One foetus was examined; length 10 cm.) The original peripheral zone of small vacuolate cells was now wider and showed a marked arrangement into two separate regions. The outer, adjacent to the capsule, consisted of small groups of cells partially separated by thin strands of connective tissue. The inner consisted of cells arranged in short radial columns, which at their outer ends were either regularly rounded off or ended against the groups of cells of the outer region. This arrangement of the cells of the original peripheral zone appears to foreshadow the development of the glomerular and fasciculate zones of the adult cortex. Internally the columns merged into the inner wide zone of densely granular, deeply staining cells belonging to the original central mass. A few large, intensely vacuolate cells with small black nuclei were still to be seen scattered among the cells of both the peripheral zone and of the inner wide zone. Practically the whole of the central region of the gland was occupied by cells of the vacuolate type, some of which, however, now possessed granular cytoplasm but still retained the small black nucleus characteristic of the vacuolate condition of the cell. Stage No. 10. (Two foetuses from different mothers were examined, each measuring 11-5 cm. in length.) The general appearance remained unchanged. In one gland, however, the continuity of the peripheral zone was occasionally interrupted by strings of the large vacuolate type of cell with small black nuclei, extending towards the centre. A few such cells were still seen in both glands scattered sparsely throughout this peripheral zone, and also throughout the inner wider zone of densely granular, deeply staining eosinophil cells. Stage No. 11. (Two foetuses from different mothers were examined at this stage of adrenal development, one measuring 12-5 cm. in length and the other 13 cm.) In the glands of this stage the peripheral zone had increased

11 ADBENAL OP THE CAT 91 considerably in width. Also a larger number of cells of the vacuolate type in the centre of the gland now possessed granular cytoplasm, whilst still retaining the small black nucleus. Stage No. 12. (See fig. 3, PL 13.) (Two foetuses from different mothers were examined, each measuring 13 cm. in length. They were apparently full-term.) The general appearance was very similar to that of Stage 11, but the inner zone of densely granular, deeply staining, eosinophil cells had decreased considerably in width. Some of the cells in the central region still possessed vacuolate cytoplasm and small black nuclei, but the majority now had granular cytoplasm, and whilst some of these still retained the small black nuclei characteristic of earlier stages, in others the nuclei had become large and palely staining. These latter cells, in spite of their granular cytoplasm and large nuclei, were clearly distinct from the cells of the original central mass, the latter being much more eosinophil, as in all previous stages of development. Thus the development of the adrenal gland of the cat during foetal life can be summarized as follows: In the earliest stage observed the adrenal anlage consists of a central mass of large, strongly eosinophil cells, surrounded by a narrow peripheral zone where the cells are smaller and less deeply staining. Cells of a third type, clearly distinguishable by their highly vacuolate cytoplasm and small black nuclei, are seen scattered in the peripheral region of the gland. As development proceeds the highly vacuolate cells gradually concentrate in the centre of the gland, whilst the original deeply eosinophil central mass is thereby being relegated to a broad zone surrounding the mass of vacuolate cells and interlocking with it. The outermost narrow zone of cells can be identified with a similar zone, described by Elliott and Armour (1911), Glynn (1912), and Cooper (1925), in the adrenal of the early human foetus, where it is claimed to be the forerunner of the permanent cortex. The large, strongly eosinophil cells obviously constitute what Elliott and Armour (1911) and Glynn (1912) call the inner portion of the foetal cortex, and what Cooper (1925) terms the boundary zone. They will be referred to henceforth in this

12 92 SAEAH DAVIES paper as the 'boundary zone'. The large vacuolate cells with small black nuclei are evidently equivalent to Cooper's sympathochromaffin cells, and will be referred to in the present paper as sympatho-chromaffin cells. Unfortunately, no foetus was obtained at a sufficiently early stage of development to show the site of origin of the different types of cells observed. By the end of foetal development the majority of the sympatho-chromaffin cells have been concentrated in the centre of the gland, but still some remain scattered in the boundary zone (see fig. 3, PI. 13). Some of those in the centre are beginning to show the characters of the typical adult medullary cells. The outermost narrow zone has become differentiated into two zones suggestive of the glomerular and fasciculate zones of the adult cortex, whilst the boundary zone remains unchanged. After birth further changes take place in the adrenal whereby it gradually assumes the adult condition. Thirteen stages of post-natal development are described below from sub-adult animals. They are arranged in what appears to be the order of development of the adrenal gland. B. Sub-adult Glands. Stage No. 1. (One sub-adult only, a female, was obtained at this stage; weight lb.) A transverse section of this gland (see fig. 4, PI. 13) showed an outer wide permanent cortex and an inner wide boundary zone interlocking with a central medulla. The cortex consisted of two zones only, an outer narrow zona glomerulosa at the periphery of the cortex and immediately within the fibrous capsule, and an inner wide zona fasciculata. The permanent cortex of this gland, and that of all glands subsequently described, was devoid of sympatho-chromaffin cells. The zona glomerulosa in section consisted of small cells arranged in groups separated by connective tissue; the cytoplasm of the cells was vacuolate, and the nuclei were pale and well denned. The zona fasciculata consisted of similar cells arranged in short columns separated by vascular connective tissue septa. The inner ends of the columns penetrated the boundary zone, but no zona reticularis could be identified.

13 ADBENAL OF THE CAT 93 The boundary zone consisted of large, strongly eosinophil cells loosely arranged in a reticular manner and without distinct cell outlines. Towards the periphery of the zone the cells were more compactly arranged, but on the medullary side they were freely intermingled with the medullary cells and formed large trabeculae. The cells of the boundary zone possessed densely granular, strongly eosinophil cytoplasm and large, pale, welldefined nuclei, only the nucleoli and nuclear membrane staining deeply. Lying freely among the granular cells of the boundary zone were seen a few large, vacuolate sympatho-chrornaffin cells with small black nuclei. The medulla consisted of a mass of cells arranged in small groups. Some of the cells were still of the typical sympathochromaffin type with vacuolate cytoplasm and small black nuclei. A larger number, however, possessed granular cytoplasm, and of these the majority still had small black nuclei, but others possessed large pale nuclei. Stage No. 2, (Five sub-adults were examined, two females and three males, all from the same litter, 48 hours old. Unfortunately they were not weighed. They were all found to be at the same stage of adrenal development.) The general appearance was the same as in Stage 1, but the boundary zone was a little narrower. Also, a larger number of the sympatho-chroniamn cells were undergoing transformation into typical medullary cells. Stage No. 3. (One sub-adult female was examined at this stage; weight lb.) This gland was similar to that of the preceding stage, but now by far the larger number of medullary cells possessed granular cytoplasm, some still retaining the small black nucleus characteristic of earlier stages whilst others had the large pale nuclei of the typical medullary cells. Some typical sympatho-chromaffin cells were still visible scattered freely among the granular cells of the medulla. Stage No. 4. (One sub-adult female was examined at this stage; weight - lb.) The general appearance was essentially the same as in pre-

14 94 SARAH DAVIES ceding stages, but the cells at the bases of the columns of the zona fasciculata, facing the centre of the gland, were loosely arranged and intermingled with the cells of the boundary zone. They were, however, clearly distinguishable from the latter, being smaller in size and having cytoplasm which was more vacuolate and less eosinophil than that of the boundary zone. A few sympatho-chromaffin cells were still seen scattered freely among the medullary cells. Stage No. 5. (Two sub-adult males were examined at this stage of development; each weighed lb.) The general appearance was as in Stage 4, but the cells at the inner ends of the columns of the zona fasciculata were now somewhat granular and more loosely arranged than previously, the whole appearance suggesting the beginning of a reticular none, but no definite zona reticularis was as yet evident. The boundary zone, in section, was of variable width, being wide in some places whilst in others it was so narrow as to be hardly distinguishable. A few typical sympatho-chromaffin cells were still evident among the medullary cells. Stage No. 6. (One sub-adult female was examined at this stage; weight f lb.) This gland presented the same essential histological picture as that of the preceding stage, but the medulla was now permeated by large irregular spaces, often containing blood capillaries. Stage No. 7. (One sub-adult female was examined at this stage. Its weight was not taken.) The boundary zone was narrower and more ill defined than in any preceding stage; moreover, it did not form large trabeculae in the medulla as in the glands previously described. A certain amount of interlocking of tissue, however, still occurred at the immediate junction of medulla and boundary zone, small groups of medullary cells lying in the intercellular spaces of the boundary zone. Again only a few unaltered sympatho-chromaffin cells were to be seen lying freely among the medullary cells.

15 ADRENAL OF THE CAT 95 Stage No. 8. (One sub-adult female was examined at this stage; weight \ lb.) As in the preceding stage a transverse section (see fig. 5, PI. 13) showed an outer wide cortex, and an inner narrow boundary zone, ill defined in places, but still interlocking with a central medulla. The majority of the cells of the zona fasciculata still possessed the pale, round nuclei characteristic of this zone in the younger stages, but in some the nuclei were now small, black, and of irregular outline, characteristic of the cells of the fasciculate layer in the adult. The cells at the bases of the columns had the same appearance as the remainder of the cells of this layer, but were loosely arranged in a definite reticulum and formed what appeared to be a very narrow, ill-defined zona reticularis between the fasciculate layer of the cortex and the remaining boundary zone. A few vacuolate sympatho-chromafiin cells were still seen in the medullary mass. Stage No. 9. (One sub-adult male was examined at this stage. Its weight was not taken.) A transverse section (see fig. 6, PI. 13) showed that the boundary zone had completely disappeared. The cortex was therefore now in direct contact with the medulla, but there was no interlocking between the two. Three cortical zones were clearly distinguishable, an outermost, narrow but well-defined, vacuolate zona glomerulosa; a middle wide zona fasciculata also vacuolate; and an innermost, narrow but clearly marked zona reticularis consisting of loosely arranged granular cells. That this is the zona reticularis and not the boundary zone is beyond question. The cells here were smaller than those of the boundary zone, had more definite cell walls, and were very much less eosinophil. They correspond exactly with the cells found at the bases of the columns of the fasciculate zone in Stage 8, where they were identified as of the reticular zone type. At that stage there was no possibility of confusing them with the cells of the boundary zone, for both regions were present together, adjacent to each other, and showed up in strong contrast to each other.

16 96 SARAH DAVIBS The medulla in section was extensive in area compared with the width of the cortex, and a few typical sympatho-chromaffin cells were still visible lying freely among the medullary cells. Stage No. 10. (One sub-adult male was examined at this stage; weight 2J- lb.) The general appearance was as in the preceding stage, but now a larger number of the cells of the zona fasciculata possessed the small, black, irregularly stellate nuclei characteristic of this zone in the adult. Also, the zona reticularis, though still narrow compared with the zona fasciculata, was relatively wider than in Stage 9. Stage No. 11. (One sub-adult male was examined at this stage; weight 2 lb.) The cells of the zona fasciculata were more highly vacuolate, and those of the zona reticularis more densely granular, than in the preceding stage. Further, the cortex in section occupied a relatively larger proportion of the gland, when compared with the medulla, than in the previous stage. A few unmodified sympatho-chromaffin cells could still be seen intermingling freely with the more typical medullary cells. Stage No. 12. (One sub-adult female was examined at this stage; weight If lb.) The zona reticularis was relatively wider than in the preceding stage, and only a very few, rather small, unmodified sympatho-chromaffin cells could be seen among the medullary cells. Stage No. 13. (One sub-adult male was examined at this stage; weight 2 lb.) The zona reticularis was now relatively much wider. Indeed, the cortex now occupied a much greater proportion of the width of the gland, in section, than in previous stages. No sympathochromaffin cells were seen among the medullary cells. Thus, during the post-natal development of the adrenal gland in the cat, the cells of the boundary zone are gradually relegated to the periphery of the medulla and finally disappear; conse-

17 ADRENAL OP THE CAT 97 quently the cortex and medulla come into direct contact with each other. Before the boundary zone has entirely vanished the reticular zone of the adult cortex makes its appearance, apparently as a differentiation of the inner ends of the fasciculate layer. It is at first narrow and ill denned, but gradually assumes the form of a definite reticular zone. The cortex then increases rapidly in width, owing largely to the greater development of this zone. With regard to the medulla, its post-natal development consists of the disappearance of the trabeculae of the boundary zone, and the transformation of all the sympatho-chromaflin cells into typical medullary cells. V. GENERAL DISCUSSION AND SUMMARY. The observations herein recorded go far to establish the homology of the inner zone of the foetal cortical tissue in the cat with the boundary zone of man. In the cat this zone disappears in early post-natal life, as it does in man, and, contrary to Soulie's claim (1903), it does not give rise to the reticular zone of the permanent cortex, this latter zone apparently arising by differentiation of the inner ends of the columns of cells of the fasciculate zone. Whether or not the boundary zone in man and in the cat is homologous with the interlocking zone in the mouse is not certain. The three tissues have the same relationship with other parts of the gland in all cases, and in all cases have the same fate of ultimate degeneration. But whereas in the mouse the interlocking zone is known to be the inner part of the original cortical mass (i.e. of the original adrenal anlage before any sympatho-chromaffin cells have invaded it), in man and in the cat the origin of the boundary zone is unknown. In both the latter cases the earliest known stage of development already shows a specialized outer zone surrounding a central mass of cells, the former giving rise to the adult cortex and the latter being the boundary zone. I wish to express my thanks to Mrs. Bisbee for the help and criticism she has given me throughout this investigation. NO. 317 H

18 98 SAEAH DA VIES LITERATURE CITED. 1. Armour, R. G., and Elliott, T. R., "Development of the Cortex in the Human Suprarenal Gland", 'Journ. of Path, and Baet.', vol Cooper, E. R. A., 'Histology of the more important Human Endocrine Organs at various ages', Oxford Univ. Press. 3. Glynn, E. E., "Adrenal Cortex its Rests and Tumours", 'Quart. Journ. of Medicine', vol Jackson, C. M., "Post-natal development of the Adrenal in Albino Rats", 'Amer. Journ. Anat.', vol Soulie, A. H., "Developpement des Capsules Surrenales chez les Vertebres Superieurs", 'Journ. de l'anat. et de la Physiol.', Paris, tome Waring, H., "Development of the Adrenal Gland in the Mouse", 'Quart. Journ. Micr. Sci.', vol Weynmnn, M. F., "Beginning and Development of Function in the Suprarenal Medulla of Pig Embryos", 'Anat. Rec.', vol. 24. EXPLANATION OF PLATE. ABBREVIATIONS. b.z., cells of boundary zone; f.c, fibrous capsule; m., medullary cells; p.z., peripheral zone; s.c, sympatho-chromaffin cells; z.f., cells of zona fasciculata; z.g., cells of zona glomerulosa; z.r., cells of zona reticularis. All thefiguresrepresent transverse sections of cat adrenals taken through approximately the middle of the gland. Bouin's fluid and Ehrlich's haematoxylin and eosin. PLATE 13. Fig. 1. Adrenal gland of a foetus measuring 3 em. in length, x 250. Fig. 2. Gland of a foetus measuring 7 cm. in length, x 215. Fig. 3. Gland of a foetus measuring 13 cm. in length, apparently full term. X 255. Fig. 4. Gland of a very young female sub-adult at Stage 1 of postnatal adrenal development, x 215. Fig. 5. Gland of a female sub-adult at Stage 8 of post-natal adrenal development, x 215. Fig. 6. Gland of a male sub-adult at Stage 9 of post-natal adrenal development, x 225.