STUDIES ON THE DEVELOPMENT OF THE EMBRYONIC OVARY IN SWINE, CATTLE AND HORSE

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In an attempt to clarify the peculiarity of the structure and function of ovary in swine, cattle and horse, the author has made comparative studies on the development of the fetal ovary dividing the pregnant period into 12 stages (Table 2). His obtained results may be briefly stated as follows : 1. The fetal ovary connected with the mesonephros in the first period gradually moves and settles in the pelvis major in the middle stages. The settlement of swine ovary is slower as compared to that of cattle and horse. This seems to be related to the size and rise and fall of the mesonephros. 2. The changes in weight and volume of the fetal ovary show a tribal peculiarity. The ovary increases its weight and volume showing an approximate straight line together with the growth of the embryo in swine and cattle, but, in the horse it shows a distinct increase up to approximately the 8th stage and thereafter decreases (Charts 1 and 2). 3. The density of the fetal ovary decreases in keeping with the weight and volume in swine ; it decreases up to the middle period and thereafter increases in cattle. No remarkable changes have been observed in horse (Chart 3). 4. The differentiation of the sex gland appears in the about 30 day old embryo in cattle, horse and swine without indicating any tribal difference. 5. The cords of PFLUGER are differentiated from the germinal epithelium. The development of the cords of the swine is more distinctive than that of the others. The degeneration of the cords begins with the beginning of growth of the primary follicle and these are only found as a vestige in the last period in swine and cattle, but are comparatively distinct in horse. 6. Cattle demonstrate the development of the primary follicle, more clearly than the others. Many primary follicles are observed in swine, but are few in horse showing a little increase after the 7th period (crown-rump-length 40cm). 7. The follicle atresia of the fetal ovary is found only in catttle ; it takes 2 forms, absorptive and vacuolar degeneration. 8. Medullary cords are formed by a part of the mesenchymal cells derived from the mesoderm. Though medullary cords swarm with the greater part of medulla at the 1st period, they are only discriminated as vestiges of the cells in the 12th period in swine and horse. 9. Interstitial cells originate in the indifferentiated germinal epithelial cell, that is, in the mesenchymal cell. They are found only in the fetal ovary of horse which is made up of an almost solid mass of interstitial cells during the major portion of the pregnancy period ; these cells are concerned with internal secretion. 10. The connective tissue in the cortex and medulla of ovary takes reticular form of which the fibers are rich in argyrophile fiber with a few collagenous and no elastic fibers. 11. The development of the blood vessels of the ovary of horse is more clear than the others. Erythroblasts in the vessels disappear at the time of appearance of artery. 12. The macroscopical changes of the fetal ovary which showed a tribal peculiarity are explained histologically. That is, in horse, the changes of the weight and volume connected with rise and fall of the interstitial cells and the stability of the density are due to the tissue which is equalized by the interstitial cells. The changes of the density of the ovary of cattle depend on the augmentation of tissue by the development of primary follicles into mature follicles. On the other hand, in swine, it seems that the connective tissue becomes loose because of the degeneration of the PFLUGER'S cords and the state of repose of the primary follicles. As indicated in the foregoing explanation, it is considerd that the peculiarity of the embryonic development in swine, cattle and horse ovaries is related to the postnatal changes of the ovary, the hormone of the placenta and the rise and fall of the mesonephros.
1955-12-15

STUDIES ON THE DEVELOPMENT OF THE EMBRYONIC OVARY IN SWINE, CATTLE AND HORSE

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