No. 2.] ANURIDA MARITIMA. 255 
maining in the yolk is undoubtedly from those cells that were 
inside the morula. As to the names to be applied to these 
determinate layers of the blastoderm there is no doubt. With- 
out hesitation the outer can be called ectoderm and the second 
mesoderm, while, as will be shown later, the entoderm develops 
from certain of the cells left in the yolk. It remains dormant, 
however, until a late stage in embryonic life. 
Precephalic Organ and Blastodermic Membranes. 
For a certain time after the blastoderm is fully formed 
further changes consist chiefly in increase in the number of 
cells and decrease in their size, the lower layer always main- 
