Abstract
To investigate the differentiation of pars anterior (principalies), pars intermedia and pars tuberalis of the hypophysis cerebri, the primordial pars anterior, removed from larvae of Bufo vulgaris fcrmosus in the early and the middle external gill stage, were grafted into normal larvae of the same animals in two different sites-the diencephalic ventricle and between lateroventral cutaneous ectoderm and mesoderm of the lateral plate. In the early external gill stage, the primordial pars anterior is attached to the protuberance of the optic chiasma, and in the middle external gill stage, it is found in the base of the diencephalon, extending from the posterior part of the protuberance of the optic chiasma to the anterior part of the infundibular wall. The primordium is perfectly independent of the mother ground.
1) When the primordium was grafted into the ventricle, the pars anterior, typical of the young larva, was differentiated from both grafts removed in the early and the middle gill stage. And the degree of the differentiation was higher in such grafts as were pressed out of the ventricle into the chondrocranial cavity or a cephalic subcutaneous part as the result of morphogenetic movement than in those which continuously remained in the ventricle.
The differentiation of parts, assumed to be the pars internedia and the pars tuberalis, could not be recognized.
2) In grafting into a lateroventral subcutaneous site, it was found that the primordium, removed in the early external gill stage, had not yet the potency of self-differentiation, and that the primordium could undergo differentiation of prospective significance for the first time in the middle external gill stage. Consequently, for the differentiation of the pars anterior, the contact with the brain for less than about 16 hours was assumed to be sufficient.
3) In the above experiments, from the graft removed in the middle external gill stage, such tissue as was assumed to be the pars tuberalis from its histological picture and morphology was differentiated in addition to the pars anterior. It is therefore considered that the pars tuberalis would acquire the potency of self-differeatiation next to the pars anterior, and that this would be dependent on the contact with the base of the diencephalon.
4) The differentiation of the pars intermedia could not be found the graft removed in either of the two stages regardless of the site of the grafting.
