NOTE ON THE DEVELOPMENT OE AMPHIBIANS. 307 
the fore-brain and the growth forward of the lower jaw take 
place at the same time, and in nearly the same extent, thus 
making the hypophysis appear as an ingrowth, whereas it is 
simply that part of the epiblast which has retained its original 
position with relation to the brain, and which has become sur- 
rounded and embedded by the expansion of the adjacent parts. 
There is another point of difference between the hypophysis of 
the Frog and the hypophysis of the Urodele embryos. In 
Amblystoma and Triton the hypophysis at the very beginning 
of its differentiation lies immediately adjacent to the posterior 
wall of the infundibulum, and later the anterior end of the 
notochord touches its posterior side. In the Frog the hypo- 
physis at first does not reach the posterior wall of the infundi- 
bulum. As it begins to loose its connection with the epiblast 
it gradually comes to lie nearer the posterior wall of the 
infundibulum, and finally lies slightly ventral to the anterior 
end of the notochord, the latter being pressed against the 
infundibulum. Thus a nearly similar condition results from 
two apparently different methods of development. In Ambly- 
stoma the position of the hypophysis is the result (mechanically) 
chiefly of a forward movement of the anterior part of the brain. 
It seems most probable that the case is the same in the Frog, 
but that the forward movement of the anterior part of the 
brain takes place at a later date. 
To GoetteV description of the other parts of the brain of 
Anura during these stages I have nothing to add. There are 
a few points, however, which may be mentioned for the sake of 
orientation as to the stages of development of the embryos 
here referred to. In a transverse section through the head of 
an embryo at the stage of fig. 20 the lumen of the fore-brain 
appears triangular, with one angle representing the dorsal 
crest of the brain, and the side opposite that angle representing 
the morphologically anterior wall of the brain. The lateral 
angles of the lumen are the beginnings of the optic outgrowths. 
In au embryo at the stage of fig. 21 the optic outgrowths are 
somewhat prolonged, and the lumen is drawn out laterally in 
1 Goette, ‘ Die Entwickelungsgescbichte der Unke,’ Leipzig, 1875. 
