No. I.] 



THE EMBRYOLOGY OF CREPIDULA. 



51 



B and D, are somewhat smaller in size, while the single polar 

 furrow remains almost as long at the animal as at the vegetal 

 pole. In the &gg of C. fornicata, which contains less yolk, 



Diagram 2. — Polar furrows of spiral cleavage. — a, The condition in eggs with much yolk 

 (C. adtmca), in which the polar furrow is as long at one pole as at the other. — b, The 

 position of the polar furrow in reversed cleavage. — c. The condition in eggs with a 

 smaller amount of yolk (C. fornicata), in which the cells A and C lie at a higher level than B 

 and D, and the polar furrow is shorter at the animal than at the vegetal pole.— (/, Egg 

 with a still smaller amount of yolk (C. plana), in which the four macromeres meet in a point 

 at the animal pole ; there is but one polar furrow, the vegetal. — <?, Egg of Discocoelis 

 (Lang), in which there are two polar furrows of nearly the same length. — f, Egg of 

 Eotryllus ; polar furrows similar to the last, but whole egg more compact. 



and which is represented in Diagram 2, c, the relation of the 

 blastomeres to each other is in the main the same as in 

 Diagram 2, a, still the macromeres A and C overlie B and D 

 to a greater extent than in the preceding diagram, and there- 



