56S 



C'KKSSWKI.L SllKAI.'Ki;. 



The blastopore ut first lies exactly in the middle of the 

 ventral plate, and is marked out behind by two lai-ge cells, 

 v.'hich, as in Nereis, probably belong to the X group (fig. 11). 

 When fully formed it is an elongated slit, somewhat enlarged 

 at its anterior end. This end never completely closes, but 

 after the formation ot" the stomach becomes the future mouth. 

 The posterior portion closes completely, the anus breaking 



Text-figs. 21 and 22. 





stmjC. 



m 



^ccc.n) 



Sections thvongli early trooliophores of Eupomatvxs. </. Gut. 

 ces. (Esophagus. /». Mouth, hh. Head kidney, cce.m. CchIo- 

 uiesoblast. xtnic. Stoniacli. 



through almost iramediatel}' at the point where the last portion 

 of this part of the blastopore disappears. Thus the closure of 

 the blastopore in Eupomatus is essentially the same as in 

 Polygordius, although the difl'erent steps intheprocess are 

 not so evident. In the majority of Annelids the blastopore 

 usually closes completely, as in Capitella. 



5. 'J' HE ECTOMKSOBLAST. 



Towards the end oP g-astrulation some irregular cells are 



