FATE OF BLASTOPORE, ETC., IX CHELONIA. 33 



him of what I wish to do in writing this paper, the best course 

 open to me would be to make him Jook through my sections and 

 to explain to him the nature of each series, (in addition to looking 

 over the embryos in toto), I feel myself obliged to adopt, in writing, 

 a course as similar to that ;is I can make it, and to pick out the series 

 of sections that are important and to describe them. I, however, 

 intend to be as brief as possible and to touch only on the salient 

 features. 



Series I. 



(PI. IV.) 



Chelonia caouana. 



An embryo, imtli no mesohlastic somites ; taken out O^jo days after 

 deposition* ; surface vieics given in Figs. 1 d- la, PL I. (b ii b). 



In this series is given a number of transverse sections from the 

 posterior portion of the Clielonia embryo given in Figs. 1 & la. 



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

 chorda in this region is distinctly formed, and is 

 independent of all the surrounding parts: the mesoblast, 

 the hypoblast, and the epiblast. 

 b is the eighth section behind a. The chorda is in the 

 process of formation but is as yet in connection with the 

 mesoblast and the gut-hypoblast. 

 C is the sixth section behind h, and is slightly in front of the 

 ventral opening of the blastoporic passage. The chorda, 

 as such, is no longer recognisable, and the 6'//o/7?rt-hypo- 

 blast, the gastral mesoblast, and the gnt-hypoblast are all 

 in connection with one another. 



* The age of the embryos given in days does not at all indicate the stage of development to 

 ■which they have attained, as this depends on the temperature of the atmosphere and other ex- 

 ternal conditions. 



