200 



THE ANCESTRY OF VERTEBRATES 



the ventral side, the distance from the animal pole to the 

 slit-like blastopore measured ventrally being much less 

 than 180°. In accordance with this the dorsal blastopore 

 lip, as fig. 6 (plate) compared with fig. 1 (plate) shows, 

 and the archenteron under it are developed strongly, the 



Fig. 41. Three eggs of Amblysfomatigrinum during the closure 

 of the medullary folds. 



a seen from behind, b dorsally, c (the same as 6) and 

 d ventrally. 

 a. anus, bl. blastopore, h.p. cerebral plate, k, head. 



ventral blastopore lip and the so-called anal diverticulum 

 very little. Yet both the latter are still quite well recognizable 

 and on the outside of the ventral lip, a little distance behind 

 the blastopore, m.iy even be noted a smill depression of 



