234 WILLIAM BATESON. 



cord. n. g. Neural groove, p. Proboscis. j)t. Point at 'which anterior body 

 cavity closes, r. 31'. Right posterior horn of anterior body cavity. (Vide 

 note below.) s. c. Segmentation cavity, sh. Shell. 



I have to thank Mr. H. A. Chapman for assisting me with the figures of the 

 surface views. 



Pig. 31« was very kindly drawn for me by Mr. W. P. R. Weldon, 

 The outlines were drawn with Zeiss's camera lucida. 



Pigs. 1 — 17. — Surface views of eggs and larvse of successive stages. 

 (Zeiss's Obj. A, oc. 2.) 



Pig. 1. — Ovum just laid, unfertilized. 



Pig. 2. — Pertilized egg. 



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

 afterwards represented. 



Pig. 4. — Blastosphoere, cell outlines visible. 



Pig. 5. — Gastrula seen from blastoporic surface. 



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



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



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



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



Pig. 10.— Older larva. (Stage C.) 



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



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



Pig. 13.— Stage E. 



Pig. 14.— Stage P. 



Pig. 15. — Stage G, from the side. 



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

 men.) Appears shortened, owing to ventral flexure. 



Pig. 17. — Stage H, from the side. 



Pig. 18. — Vertical section through centre of a late blastosphoere. (Zeiss's 

 Obj. D, oc. 2.). 



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



Pigs. 20 and 21. — Sections through the blastopore of gastrulte in two 

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



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

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



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



[Note. — In interpreting those figures in which the right and left sides of 

 the animal are indicated, it must be remembered that as the figures are traced 

 as seen through the microscope, the position of the real right and left sides is 

 reversed.] 



