一種の山赤蛙Rana tagoi OKADAの發生特に胚の適應形質に就て

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This mountain frog distributes rather restictively in Japan proper. In the vicinity of Kyoto its spawning lasts from the end of May to the middle of June, with, of course, some deviations according to the conditions of the climate of the year. But it corresponds roughly to the rainy season of the locality. Eggs are laid in a sharrow pool temporarily made after rain or at the bottom of a small cave excavated by the crab or produced after the disappearance of a rotten root. They are, therefore, obliged to develop quickly in order the larvae to leave the recess before the water drys up. For this purpose embryos show remarkable features of adaptation: 1) Eggs in a mass are separated each other by jelly bridges to insure against the oxygen-shortage. 2) The medullary plate appears as early as the yolk-plug still persists. 3) Both fore-and hind-limbs appear as soon as gills become recognizable, and they grow and differentiate ceaselessly. The differentiation of a limb bud into upper and lower parts is observed 8 days after oviposition. 4) The internal gills appear while the external ones are still developing, and thus two kinds of gills are present externally at the same time. Erythrocytes may be more suitable for the respiration than erythroblasts, but this differentiation does not keep pace with the development of gills in the present frog as in the Chinese Kaloula, which undergoes also a rapid development in the temporary pools. 5) Contrary to the mentioned overlapping hurried formation of the external organs, the differentiation of the alimentary tract takes place remarkably later and slowly; the stomach, duodenum and rectum being formed earlier than the other parts of the intestine. The coils of the latter are few in number and in their highest development we count only five turns (fig. 2, E). At the time of metamorphosis, histolytic process beings in the mid-intestinal region; the larval epithelium being shed off into the lumen to be replaced by the reparative cells which are scattered here and there among the old ones at the basis (fig. 5). But in the duodenal and rectal regions, most of the larval cells transforms directly into the adult ones. 6) Yolk is abundant enouth to nurish the tadpole throughout the whole larval life. During metamorphosis, acinar cells of the pancreas exhaust rapidly their yolk granules and some of them degenerate; therefore the pancreas of the young frog is far smaller than in the tadpole (fig. 2, E' and I). But the liver shows no apparent difference before and after metamorphosis; the yolk granules are exhausted long before, and very little degeneration of cells takes place. 7) The differentiation of gonad occurs before metamorphosis, and the present frog belong to the sex-differentiated race. In closing the description, as the factors, which are here related to the rapid development of the frog in question, may be mentioned temperature-rise, oxygen-consumption and the thyroid-hormone, ctc. Each of them is, indeed, responsible to the phenomenon as a whole, but at the same time any of them is hard to be regarded as the reason of the overlapping differentiation of organs which are, as a rule, formed one after another. The early secretion of the thyroid hormone is, for example, related to the rapid growth of limbs, but the early differentiation of the gonad cannot be explained by the same reason. We may suppose another type of factors, the nature of which is unfortunately undetermined. The tadpoles takes about 22 days or so, at most 25 days, from oviposition to complete metamorphosis at the temperature 19℃-25℃ in the laboratory. Here I wish to acknowledge my indebtedness to Prof. Yo K. OKADA for his kindness of revising the manuscript.
1938-02-15

一種の山赤蛙Rana tagoi OKADAの發生特に胚の適應形質に就て

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