446 



SUPPLEMENT. 



Chapter V. 



SUPPLEMENTARY NOTES ON THE MOLLUSCA. 



Class, I. Cephalopoda. 



Levelopment, (p. 54.)— "All that is at present known upon this subject, 

 is contained in the very beautiful memoir by Kolliker, who gives au elaborate 

 account of the development of Sepia, Loligo, and Argoyiauta* 



" The process of yolk-division is partial, and the development of the 

 embryo takes place within a distinct germinal area — whence a distinct yolk- 

 sac is formed. This is proportionally very large in Sppia (Fig. 229) and Loligo, 

 very small in Argonauta (Fig. 230) and therefore while the embryo is flattened 

 and extended in the former genera, in the latter it more resembles the embryo 

 of au ordinary Gasteropod. 



" Development commences by the separation of the embryo into mantle 

 and bodg, (foot). The ])art of the body m front of the mantle becomes the 

 liuad ; that behind it becomes the branchio-anal surface. 



Fig, 229. Development of the Cuttle-Jish. (Kolliker.) \ 



A. Embryo two lines in diameter; m. mantle ; 6, branchial processes ; «, siphonal 



processes; a, mouth ; e, eyes; 1 — 5 rudimentary arms. m 



B. Side view of the embryo, when more developed. ■ 



C. Front view, at a later period. Iti 



D. Young cuttle-fish, still attached to the yolk-sac, with the tentacular qitub (2)^1 



longer than the rest. 



"The latero-posterior margins of the body are produced into four or five ^ 



processes on each side, which become the arms. } 



" On each side of the mantle, between it and the head and arms, a ridge 



Entwickelungs geschichte der Ceplialopcden. Zurich, 1844. 





