158 WILLIAM BATESON. 



Fig. 3. — Egg segmented into two by a median furrow. The eggshell is not 

 afterwards represented. 



Fig. 4. — Blastosplicere, cell outlines visible. 



Fig. 5. — Gastrula seen from blastoporic surface. 



Fig. 6. — Later gastrula ; blastopore contracted, seen from the side. 



Fig. 7. — Closing gastrula, seen from the mouth ; ciliated. (Stage A..) 



Fig. 8. — The same seen from the side. 



Fig. 9. — Larva shortly after the blastopore has closed, from side. (Stage B.) 



Fig. 10.— Older larva. (Stage C.) 



Fig. 11. — Stage D. (Drawn from a preserved specimen.) 



Fig. 12. — Larva between Stages D and E. 



Fig. 13.— Stage E. 



Fig. 14.— Stage F. 



Fig. 15. — Stage G, from the side. 



Fig. 16. — Stage H, from dorsal surface. (Drawn from a preserved speci- 

 men.) Appears shortened, owing to ventral flexure. 



Fig. 17. — Stage H, from the side. 



Fig. 18. — Vertical section tlirough centre of a late blastosphoere. (Zeiss's 

 Obj. D, oc. 2.). 



Fig. 19. — Section through plano-convex blastosphoere. (Obj. C, oc. 2.) 



Figs. 20 and 21. — Sections through the blastopore of gastrulee in two 

 stages. (Obj. C, oc. 2.) 



Fig. 22. — Transverse section through a closed gastrula, between Stages 

 A and B. (Obj. B, oc. 2.) 



Fig. 23. — Transverse section through the anterior end of a larva, between 

 Stages C and D. The letter H is placed in the arclienteric cavity. (Obj. D, 

 oc. 2.) 



Fig. 24. — Transverse section through posterior end of the same larva as the 

 preceding. The transverse band of cilia and the point at which the blasto- 

 pore has closed are cut through. (Obj. C, oc. 2.) 



Fig. 25. — Longitudinal median vertical section tlnoufjh same larva as pre- 

 ceding. Constructed from tiie series of transverse sections, in which those 

 represented iuFigs. 23 and 24 occur. 



Figs. 26 — 34 represent some of a series of transverse sections taken through 

 a larva in Stage E. The epiblast is represented diagrammatically. In each 

 case the upi>er side is the dorsal one. (All, excepting Fig. Zla, were drawn 

 with Obj. D, oc. 2.) 



Fig. 26. — Section through prseoral lobe, showing the amoeboid cells forming 

 the wall of the mesoblastic sac. 



Fig. 27. — Section through the foramen, by which the anterior body cavity 

 opens into the archenteron. The space lying ventral to the hypoblast is the 

 slight ventral backward prolongation of the anterior body cavity, which would 

 diaappear in the next few sections. 



