FATE OF BLASTOPORE, ETC., IX CHELOXIA. 39 



entirely di.sappeared, excepting' ;i little .stretch on the left. 

 h is the section next to ij. The epil)last now extends over 

 the entire breadth, hut there is still :i mass of cells in the 

 median line, immediately below the epiblast, which is 

 connected Avith the superjacent epiblast and with the 

 subjacent mesoblast. This mass, which I have darkened, 

 in the figure from conventionality, is in fact lighter and 

 quite noticeable. It gradually decreases until in the fifth 

 sections Ijehind //, the epiblast is distinctly separate 

 throughout from the mesoblast IdcIow, and thus the three 

 layers become all independent. 



The obliquity of the blastoporic passage, which has now become 

 the neurenteric canal, is much less in this series than in Series I. 



Fig. 9 (PL 11.) of Cleiumi/s and Fig. 2 (Fl. I.) of Chelonm are the 

 stages corresponding to this in Trionyx. The main points of these 

 embryos are like tliose of this series, although different in various 

 details, since the idiosyncrasies of individual embryos not only in 

 different species but within the same species are as a general thing 

 very great. 



Series III. 



(PI. n.) 



Clcmwys japon im . 



An cmliryo with 5 mcsohlastic somites ; tal^cn out 4^/2 days after deposi- 

 tion ; represented in Fi<j. 10, PI. II. ( = Contrib. II., Plate I., Figs. 2 

 and 2a). (xxxxix). 



In this is üiven a series of transverse sections throuo-h the 

 posterior part of the Cleinmys embryo represented in Fig. 10. The 

 yolk-plag has already receded a little from its original position. 



a is from the hinder portion of the mid-dorsal region. The 

 medullary canal is still open. 



