PLATE 14. 

 Fig. 26. — A section of the margin of the mantle taken through an eye. 

 The section is taken rather near the hinge line on .the pos- 

 terior border, in a plane nearly corresponding with the line 

 pa., Fig. II. Most of the circular muscles leave the infolded 

 ridge ventral to this point, and there are no tentacles on the 

 ridge at this level. Magnified about fifty diameters. 



PLATE IS. 



Fig. 27. — ^An egg at the time of the formation of the second polar body 

 showing the yolk lobe. Magnified about seven hundred diam- 

 eters. 



Fig. 28. — Two-celled stage after the yolk lobe has disappeared. Magni- 

 fied about seven hundred diameters. 



Fig. 29. — ^Two-celled stage soon after cleavage showing the yolk lobe. 

 Magnified about seven hundred diameters.' 



Fig. 30.-^Four-celled stage. Magnified about seven hundred diameters. 



Fig. 31. — Eight-celled stage. Magnified about seven hundred diameters. 



PLATE 16. 



Fig. 32. — Later cleavage stage. Magnified about seven hundred diam- 

 eters. 



Fig. 33. — A sagittal section of a slightly later stage than that shown in 

 the preceding figure. Magnified about seven hundred diam- 

 eters. 



Fig. 34. — A somewhat later stage seen as a transparent object from the 

 left side. Magnified about seven hundred diameters.- 



PLATE 17. 



Fig. 35.— Veliger larva seen as a transparent object from the left side, 

 with the velum extended. This stage is reached in about 

 thirty hours after the egg is laid. The one figured is slightly 

 older than this. Magnified about seven hundred diameters. 



Fig. 36. — ^Veliger larva seen as a transparent object from the anterior 

 end. Magnified about seven hundred diameters. 



71 



