FURTHER STUDIE8 OX THE GERMIXAL LAYERS ETC. 51 



chovdii-aitlatfe gets incorporated in tlie mesoblast, and the parts external to 

 these sliaded portions become tlie gut or definitive hypoblast. This should l)e 

 compared with the section of Amphioxus reproduced in Fig. 39. BBx4. 

 Fig. 12. Transverse section I'lom the anterior part of tlio Clemniys embryo 



■ represented in Figs. 3 and 4rt. DD x 2, 

 Ficjs. lS-22. Selected transverse flections from the Cloramys embryo given in 

 Fig. 2. DDx2. 



Fi(js. IS-IH. — From the anterior part, show the manner in which the gastral 

 mesoblast extends itself forwards. The gut-hypoblast is at a consider- 

 able distance from the chorda-««/«^/,'. The lightly shaded part is the 

 part of the originnl primitive hypoblast that becomes incor[)orated in 

 the mesoblast. The darkly shaded part represents the mesoblast mass 

 which has been budded out from the lightly shaded part. 

 Fig. 17. — The gut-hypoblast has extended itself inwards to the chovA-A-anlage. 

 Fig. 18.— A little behind Fig. 17. The chorda, the mesoblast and the gut- 

 hypoblast have separated from one another. 

 Fig. 19. — Further behind. The three structures have again united. 

 Fig. 20. — Directly in front of the ventral opening of the blastoporic 



passage. 

 Fig. 21. — Through the blastoporic passage. 

 Fig. 22. — Through the yolk-plug. 



Plate IV. 



Figs. 23-o2. — Selected tra.nsverse sections from the Clemmys embryo given in 

 Figs. 4 and 4«. DD x 2. 



Fig. 2S. — Through the head region and the gut-diverticula. See the ventral 



surface view, Fig. 4«. 

 Fig. 24. — Tliird section behind. 

 Figs. 25-28. — From the middle region of the body, showing the formation of 



the notochord. 

 Figs. 29 é SO. — In front of the ventral opening of the blastoporic passage 



The c\\oxài\- anläge, the mesoblast, and the gut-hypoblast have again 



united with one another. 

 Fig. 31. — Through the blastoporic passage. 



