兩棲類心臟原基發生ニ關スル研究補遺

Investigations dealing with the problems on the early stages of development of the heart of the toad, have left very little for further study except the question of the origin of the angioblast. However on the development of the heart of the giant salamander, there are on record only a few experiments which are, as yet, far from satisfaction. Consequently Prof. Shikinami gave me the problem on the first appearance and the further developmental stages of the heart primordia in the amphibia, especially on the difference between these two species of the amphibia (urodela and anura). From many embryos, thirteen giant salamanders and twelve toads were selected and used for this study. A large majority of them were fixed in Zenker's fluid, and stained with borax carmine. After the subsequent treatments in the usual manner, these specimens were embedded in paraffin, trimmed and cut in transverse serial sections with a thickness of ten microns. A number of models were prepared according to Born-Peter's method of wax-plate reconstruction. From the results of these experiments, the following summary and conclusions may be made: 1) The heart primordia in the amphibia is formed from the bilateral primordia which are derived from the cardiogenic plate. 2) In the giant salamander, the pericardial cavity and the angioblast first appear in an embryo with 12-13 somites, and the ventral and the dorsal mesocardium are first formed in 17 and 20 somites stages respectively. The ventral mesocardium is more defined than that of the toad. The bending of the heart is first indicated in an embryo with 22-23 somites and the blood-corpuscles first appear in the heart in the 28-29 somite stage. 3) In the toad, the pericardial cavity first appears in an embryo with 8 somites and it is earlier than the first appearance of the angioblast, since the latter is first distinguishable in the 5-6 somite stage. The formation and the rupture of the ventral and the dorsal mesocardium are indicated a little earlier than in the giant salamander. The time of the first appearance of the blood-corpuscles in the heart and the bending of the heart, is also somewhat earlier than the latter.