246 K. MITSUKUKIAND C. ISHIKAWA. 



Fig. 16. — Median longitudinal section of an embryo closely similar to Fig. la 

 and b, and from the same deposit. 



Fig. 17. — Section passing through the ventral opening of the blastoporic 

 passage of the embryonic shield, similar to that given in Fig. 2« and b, and from 

 the same deposit. 



Figs. 18 — 23. — Series of transverse sections of an embryonic shield, closely 

 like that given in Fig. 3, and from the same deposit. Arranged from behind 

 forward. 



Fig. 18. Section passing through the lateral limbs of the horseshoe shaped 



blastopore. 

 Fig. 19. Section through the blastoporic passage. 

 Fig. 20. Section passing slightly in front of the ventral opening of the 



blastoporic passage. 

 Figs. 21 and 22. Sections passing through the middle region of the shield. 

 Fig. 23. Section passing through the region of the head-fold. 

 Fig. 24. — Median longitudinal section of an embryonic shield, closely like 

 Fig. 3, and from the same deposit. 



Figs. 25 — 28. — Series of transverse sections through the head region of the 

 embryo represented in Figs. 4a and b, ihustrating the mode of the formation of the 

 notochord. Arranged from before backward. 



Fig. 29. — Transverse section through the head region of another embryo, 

 closely like Figs. 4a and b, from the same deposit. 



î'iGS. 30 — 34. — Series of transverse sections from the posterior region of an 

 embryo, very much like that given in Fig. 4a and b, illustrating the mode of the 

 formation of the notochord in that region. Arranged from behind forward. 



Fig. 35. — Series of transvers sections from the posterior region of an embryo, 

 with five or six mesoblastic somites, showing the neurenteric canal. Arranged 

 from before backward. 



