48 K. MITSUKURI AND C. ISHIKAWA. 



Fig. 7. Section of the region where the three germinal layers are free 



from one another. 

 Fig. 8. Section of the primitive streak. 

 Fig. 9. Section passing directly behind the blastopore. 

 Fig. 10. Section passing just in front of the dorsal lip of the blastopore 

 Fig. 11. Section through the blastoporic passage. 

 Fig. 12. Section passing through the posterior part of the ventral opening 



of the blastoporic passage. 

 Fig. 13. Section passing through the anterior part of the ventral opening 



of the blastoporic passage. 

 Figs. 14 and 15. Sections passing in front of the ventral opening of the 



blastoporic passage. 

 Fig. 14«. Section showing the shelf-like extension into the archenteron. 

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

 1« 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. 4« and b, illustrating the mode of the forma- 

 tion of the notochord. Arranged from before backward. 



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

 closely like Figs. 4<2 and b, from the same deposit. 



Figs. 30 — 34. — Series of transverse sections from the posterior region of 

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

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

 forward. 



Fig. 35. — Series of transverse sections from the posterior region of an 

 embryo, with five or six niesoblastic somites, showing the neurenteric canal. 

 Arranged from before backward. 



