No. 3-] THE GASTRULATION OF AMPHIOXUS. 



575 



to determine in what region the bending in of the wall takes 

 place. The method of closing cannot, therefore, be determined 

 by any one criterion, but all the observed results must be taken 

 into account. 



It should be noticed that in these figures the dorsal {d) and 

 the ventral (v) lips of the blastopore are, throughout the early 



Figs. I-XX. 



Stages, equally distant from the point of greatest curvature {a). 

 If, on the other hand, the bending took place nearer the dorsal 

 or the ventral lip, one side would be shorter and the other 

 longer ; and this is not the case. 



Hatschek figures one side — the ventral — as longer than 

 the other side, — the dorsal, — but the dorsal subsequently 

 grows in length until it is approximately the same length as 



