No. 3.] BASIS OF THE AMPHIBIAN EMBRYO. 475 
ITI. 
Experiments 33-36 indicate that in Acris an area lying just 
above the point at which the blastopore first appears later forms 
a portion of the posterior end of the embryo. 
Experiments 41-45 gave the same results in Bufo. 
Experiments 73-83 show the same to be true of Amblystoma. 
EV. 
(2) Experiments 19-22, 28-30 indicate that in Acris the 
cells immediately above the dorsal portion of the blastopore 
pass toward and into the blastopore. 
Experiments 73-75, 77-79, 84-86 show the same results in 
Amblystoma. 
(4) Experiments 23, 24 indicate that in Acris the cells on 
either side of the blastopore approach the same and are infolded. 
Experiments 93-98 show the same to be true of Amblystoma. 
(c) Experiments 25-27, 31, 32 indicate that in Acris there 
is an infolding of the larger cells forming the yolk plug, or that 
this mass is being overgrown by the smaller cells forming the 
blastoporic margin, or that both processes are combined. 
Experiments 88-92 lead to the same conclusion regarding 
Amblystoma. ; 
Experiments 84-86 show that an infolding of the smaller 
cells forming the blastoporic margin actually takes place, but is 
obscured to a great extent by the extension or overgrowth of 
the blastoporic margin over the yolk, which is going on at the 
same time. 
Some General Remarks. 
In order to obtain a clearer conception of the factors which 
determine the position of the embryo, it is necessary to recall 
that during the cleavage of the amphibian egg the cells at the 
upper pole divide most frequently, and give rise to an area of 
smaller cells, which, according to my earlier experiments, as well 
as those recorded under I, in the present paper, forms the basis 
of the cephalic end of the embryo. 
