ニホンアカガエルRana japonicaの背中腺

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1.The dorsal gland of the present species is almost similar both in structure and in mode of development, to that of Rana temporaria ornativentris which has already been studied by myself (Yanai.'52). The T-shaped dorsal gland derived from the neural crest is divisible into two parts: a mid-dorsal division extending from the epiphyseal region to the end of the trunk, a little more caudad than in R.temp.ornat., and a frontal division with two lateral branches extending from the anterior end of the mid-dorsal division to the eye-cups. The gland, composed of about 400 glandular cells, is rather poorly developed. The glandular cells, sparsely distributed in the gland from the beginning of its development, are low in height and densely pigmented. The retrogression takes place postero-anteriorly in the mid-dorsal division as in other anurans, the first sign of which, however, appearing rather earlier in the present species, i. e., before the onset of degeneration of the external gills. The frontal division is left unaffected until later. After the tadpoles have passed the late external-gill stage (8mm in length) the whole gland begins to degenerate suddenly, and in the 15mm-tadpoles with rudiments of hind limbs the dorsal gland has gone. 2.The time of hatching is remarkably affected by temperature of water in which the embryo has continued its development. At higher temperature, it hatches out as a tadpole about 3.2mm in length without any rudiment of external gills, whereas at lower temperature, as a tadpoles approximately 7.4mm in length bearing fully developed external gills. Rigardless of water temperature, the dorsal gland always begins to secrete when the embryo has grown about 3.0mm in length. Careful histological study reveals, however, that the gland is secreting more actively at higher temperature. This fact may be responsible for the earlier occurrence of hatching in warm water. 3.The modes of movement effected by the embryo are similar to those observed in R. temp. ornat. The chorion is always pushed open by wriggling movements of the embryo. On way of gliding out of the chorion by means of the locomotive force effected by epidermal cilia, the embryo makes again several wriggling movements, the last one of which brings it at once outside the jelly coat. Some embryos, however, emerge from the chorion tail first. They become free solely by wriggling movements. Temperature at hatching does not exert any remarkable effect either upon the mode of hatching or upon the time necessary for the whole course of the process. 4.It has been found that the filtrate of medium in which a number of tadpoles have passed the late external-gill stage, is always potent in dissolving the jelly coat of young embryos and making them free. The filtrate of medium containing pilocarpine in 0.5 per cent is especially active. The filtrate becomes inactive after boiling, whether it may contain pilocarpine or not. Taking the results of the experiment and the histological findings on secretory activity of the dorsal gland into consideration, it seems highly probable that the secretion of the gland of the early hatched tadpoles facilitates hatching of batch-mates still remaining in the jelly coat.
社団法人日本動物学会の論文
1952-06-15

ニホンアカガエルRana japonicaの背中腺

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