The American Mrtsrunt of Xatural History and the College of the C i t y of New Pork.
ONE PLATE (NINE FIGVRES)
IXTRODUCTION
Several experimenters have been led to consider that, in Amphibia, the differentiation of the epithelial hypophysis is dependent upon neural contact. Thus Burch ( '38) found that the removal of presumptive infundibular areas from the gastrulae of a tree frog resulted in the failure of the differentiation of the adenohypophysis. I n extensive transplantation work with the pituitary primordium, Blount ('32) had considerable success in obtaining pituitary differentiation when brain was transplanted with the primordium. Without brain, however, he did not secure differentiation. On the contrary, I reported (Etkin, '35, '41) differentiation of the pituitary primordium without the appearance of brain tissue in the graft in tadpoles. Atwell ('35) repeated the experiments of Blount and myself with both salamander and .frog and was able to confirm both reports. It thus appeared at the time that the difference between the two species was genuine. However despite the apparent agreement at that time that in the salamander, if not in the frog, differentiation of the epithelial lobes requires contact with nervous tissue, it is none the less clear that failure to secure differentiation of the isolated primordium is not completely satisfactory evidence of dependent development. F o r it is obvious that the smaller size of the grafted piece, and other purely operative factors may A preliminary note on this experiment was given in Etkin ( '40). 3 1