50 k. MITSUKURl. 



Explanation of Figures. 



Plate II. 



Piq I — Dorsal view of a Clemiuys embryo tüken out 1 hour after its deposition. 



Zeiss aa x 2. (xxxv) 

 Fig. la. — Ventral view of tlie same, aa x 2. 



Fig. 2. — Ventral view of a Clemmys embryo 3 days old. aax2. (xxxvid. 

 i^'/V/. 3. — Dorsal view of a Clemmys embryo 3 days old. aax2. (xxxvii). 

 Fi(j. Sa. — Veulral view of the same. The head-fold marks definitely the anterior 



end of the embryo, aa x 2. 

 B'i(j. 4. — Dorsal view of a Clemmys embryo 3 days old. aax 2. (xxxxvm). 

 Fir/. 4a. — Ventral view of a Clenjmys embryo 3 days old, from the same deposit as 



Fig. 4. Note the two depressions, one on each side, immediately behind the 



head-fold and partly covered by it. These depressions are the diverticula of 



the enteric cavity seen in Fig. 23. aa x 2. 



Plate III. 



Fic). 5. — Longitudinal section of the Clemmys embryo represented in Figs 1 and 



1« near the median ventral line. BB x "2. 

 Fig. 5a. — Part of Fig. 5 more highly magnified. DD x 2. 



Fig. 6-10. — Selected transverse sections from a Clemmys embryo from the same 

 deposit aud of the same sta^e as Fig. 1. BB x 4. (xxxva). 



Fig. 6. — From directly behind the dorsal opening of tlie blastoporic 



passage. 

 Fig. 7. — Still nearer the dorsal opening of the blastoporic passage. 

 F'^ig. 8. — Through the blastoporic passage. 



Fig. .9. — Anterior to the ventral opening of the blastoporic passage. 

 Fig. 10. — Through the anterior part of the embryonic shield. 

 F^ig. 11. — Transverse section somewhat in front of the ventral opening of the 

 blastoporic passage. From a Clemmys embryo a little more advanced than 

 Fig. 1. This is introduced to show the destiny of different parts of the lower 

 layer (or primitive hypoblast) : the median unshaded part becomes eventually 

 the notochord, the lightly shaded part on each side immediately outside the 



