FATE OF BLASTOPOEE, ETC., IX CHELOXIA. 57 



matically represented, the figure of the primitive streak and groove 

 will be as in Woodcut VIL This is exactlv like the fio-ure of 

 the blastopore which Sedgwick figures in his notes on the Elasmo- 

 l)ranch ('92, p. 564). The significance of this will be discussed 

 later on. 



Series X. 



(PI. VIII.) 



Glcmmijs japonica. 



An cmhryo tvith ahout 10 mesohlastic somites; talien out 6^]o days 

 after deposition. (Lj. H). 



This embryo was taken out at the same time from the same deposit 

 as that represented in Fig. 14, but it is greatly different from that 

 fio;ure in re^rard to the backward Droi^ress of the amnion. That mem- 

 brane lias not only extended over the entire embryo but produced itself 

 backwards for a distance equal to about one-third of the length of the 

 embryo as the posterior tube of the amnion, which remains very wide 

 in this specimen, being hardly reduced in width compared with the 

 part over the posterior part of the embryo. The ventral view of the 

 embryo is very nmch like Fig. oa : only the shape of the ventral 

 opening of the neurenteric canal is spindle-shaped, instead of being 

 dumb-bell shaped, as in that figure. 



This is consideraljl}^ younger than the Clielonia embryo of Series 

 IX. It and the next series are introduced mainly to illustrate the 

 process of the u])heaval of the tail-swelling. 



a is from the posterior part of the dorsal region. The 

 medullary chord and the notochord show^ the first signs 



