160 MANUAL OF THE MOLLUSCA. 
certain parts of the palpi of the males are developed into spoon- 
shaped organs which perform the same office 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 young argonaut has 
no shell. M. Duvernoy has shown that the embryo argonaut 
has acquired a shell before it has been excluded from the egg. 
The most important memoir on the development of Cepha- 
lopods is that by Kolliker.* ‘‘The process of yolk division is 
partial, and the development cf the embryo takes place within 
a distinct germinal area, whence a distinct yolk sac is formed. 
This. is proportionally very large in Sepia (Fig. 85), and 
Loligo, very small in Argonauta (Fig. 36), and therefore while 
the embryo is flattened 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. 25. Development of the Cuttle-fish. ({Kolliker). 
A, Embryo two lines in diameter; m, mantle; 6, branchial processes; s, siphonal 
processes; a, mouth; e, eyes; 1—65, rudimentary arms. 
B, Side view of the embryo, when more developed. 
C, Front view, at a later period. 
D, Young cuttle-fish, still attached to the yclk-sac, with the tentacular arms (2) 
onger than the rest. 
embryo into mantle and body (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 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 is formed upon the body. 
These ridges (s s, Fig. 35, A), represent the epipodiwm; their 
* Entwickelungs-geschichte der Cephalopoden. Zurich, 1844, 
