.160 



MAKtAL OF THE MOLLtJSCA. 



certain parts of the palpi of tlie maJes are developed into spoon- 

 shaped organs which perform the same offi.ce as the hecto- 

 cotylus. Something similar also occurs in Polydesma. 



Madame Power appears to have made her observations on 

 an hectocotylus when she asserted that the yonng argonaut has 

 no shell. M. Duvernoy has shown that the embryo argonaut 

 has acquired a shell before it has been excluded from the eg^. 



The most important memoir on the development of Cepha- 

 lopods is that by Kolliker. * ' ' 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 Sepia (Fig. 35), and 

 Loligo, very small in Argonauta .(Fig. 36), and therefore while 

 the embryo is jflattened and extended in the former genera, in 

 the latter it more resembles the embryo of an ordinary gas- 

 teropod. Development commences by the separation of the 



Fig. 33. Development of the Cuttle-fish. (KiiUiker). 



Ai Einbl^^o two lines in diameter; m, mantle; b, branchial processes; s, siphonal 



processes ; a,, mouth ; e, eyes ; 1 — n, rudimentary ai'ms. 

 JB, Side view of the embryo, when more developed. 



C, Front view, at a later period. 



D, Young cuttle-fish, still attached to the yolk-sac, With the tentacular arms (2) 



longer than the rest. 



embryo into mantle and hody (foot). The part of the body in 

 front of the mantle becomes the head; that behind it the 

 branchio-anal surface. The latero-posterior margins of tho 

 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 is formed upon the body. 

 These ridges [s s, Fig. 35, a), represent the eptpodium; their 



* Entwickelungs-geschichte der Cephalopoden, Zurich, 1844. 



