イモリTriturus pyrrhogasterの前額腺(その二)
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概要
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1.My previous conclusion in anurans (Yanai, '50, '51) that the frontal gland is derived from the neural crest is confirmed in the present species as well. The development of the gland in the newt goes on very slowly. Whereas in the anurans the gland is formed and begins to secret as soon as the neural folds grow together, in the newt the gland cells are not yet distinguishable from the epidermal cells at the similar stage of development. Shortly before hatching, however, the gland becomes active suddenly and produces a copious secretion. 2.The gland lies on the frontal aurface of the head, and extends laterally to the anterior margin of the eyes. In the glandular area 400-450 glandular cells filled with secretory granules are scattered separately in the epidermis. The secretory granules in the cells are much larger in size than in anurans. 3.After hatching the gland decreases in secretory activity and eventually undergoes degenerations. Concurrently with the retrogression of the gland the balancers are absorbed. In the larvae which have lost the balancers no trace of the gland is encountered. All the glandular cells disappear and none of them transforms into any other sort of cell. 4.Toward the end of the embryonic life, the egg membrane, which consists of three layers, swells remarkably and is highly softened. Excepting the innermost part of the outer layer, the egg membrane has been torn. The fact that the frontal gland is at its height of secretory activity at this stage and begins to regress immediately after hatching of the tadpole suggests that the enzymic secretion of the gland is chiefly responsible for the above-mentioned changes of the egg membrane as has been demonstrated experimentally in other amphibians. No other tissue is found which attains maximum of secretory activity at the time of hatching and undergoes degeneration soon later. 5.Just befor hatching, the embryo makes several undulations for a few seconds. The headl drawn foreward against the softened egg membrane finally bursts it open. The embryo now rushes out of the egg membrane, perhaps aided by the enormously high pressure inside.
- 社団法人日本動物学会の論文
- 1952-08-15
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