534 THE AMERICAN NATURALIST. [Vor. XXXVI. 
“ physiological activity " other than that attendant upon rapid 
cell division must produce the pigmentation in these cells. 
The extension of the lateral lips of the blastopore and the 
formation of the yolk plug have been so frequently described 
for other forms that a description of these processes is not 
necessary here, as they are apparently similar in all respects 
to those which take place in the frog. Following the method 
used by Pfliiger (20), a number of eggs in the blastula stage 
were placed on a mirror in a shallow dish of water and the for- 
mation of the blastopore watched in mirror image. Figs. 1-8 

Fic. 13. — Part of a frontal section through tl ior end of th 
Fic. 2. showine li Ext 1i oci 
5 rS 5 

+. +h 
A R., archenteron. 

show the appearance and the location of the blastopore at dif- 
ferent times during the day, from 8 a.m., when the blastopore 
lip first appeared, to 6 P.M., when the egg began a rotation 
around its horizontal axis. There was no evidence to show 
that the position of the eggs was changed during the time 
they were kept under observation; on the contrary, one egg, 
in which a peculiar light spot was seen below the equatorial 
region, was watched particularly, and the spot was found to 
keep its same relative position until the rotation of the ess 
took place. These mirror images show that the dorsal lip of 

