22 2 CONK LIN. 



EXPLANATION OF PLATE VII. 



Fig. 74. Dorsal view of an embryo of C. fornicata. The apical cells lie at 

 the anterior margin of the figure, the dorsum is covered by the large cells of the 

 posterior cell plate, the shell gland is forming on the postero-dorsal surface a 

 little to the left of the mid line. The four macromeres and the polar furrow are 

 still recognizable. 



Fig. 75. Embryo similar to the preceding, but showing the invagination of 

 the shell gland. 



Fig. 76. Ventral view of an older embryo, showing the beginnings of the nerv- 

 ous system and the laeotropic torsion of the intestine. The foot is appearing as 

 a prominent area posterior to the mouth. 



Fig. 77. Side view of same embryo, showing the branching of the velum on 

 each side of the posterior cell plate, and the relation of the intestine to the shell 

 gland and foot. 



Fig. 78. Side view of older embryo, showing head and foot vesicles, apical 

 plate and organ, cerebral ganglia and commissure, posterior and pedal cell plates, 

 anterior and posterior branches of the velum, expanding shell gland, external 

 kidney, stomodaeum and mesenteron. 



Fig. 79. Apical view of same stage, showing apical, posterior and pedal cell 

 plates, pre- and post-oral velum, apical organ and cerebral ganglia. 



Fig. 80. Side view of older embryo. Intestine carried up on right side and 

 opening at its proximal end into cavity between the yolk cells. Intestine sur- 

 rounded by single layer of cells inclosing a clear cavity. 



Fig. 81. Ventral view of similar embryo, showing circum oesophageal nerve 

 ring, pre- and post-oral velum, etc. 



Fig. 82. Apical view of still older embryo, showing pre- and post-oral velum, 

 ocelli, otocysts, etc. 



