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latter are little cases filled with spermatozoa ; when these 
cases are moistened, they burst, and expel their contents. 
In the male cuttle fishes, one of the brachia becomes 
altered, an oval sac is developed, and filled with spermatazoa ; 
this process is called hectocotylisation. In some species the 
hectocotylised arm is detached and left in the mantle- 
cavity of the female, when the spermatophores, becoming 
ruptured, the male elements have access to the ova, and 
fertilise them. 
The male of the Argonaut has no shell, and is only about 
an inch in length ; one of the arms is developed into a sac- 
like body containing a hectocotylus, which, by its movements, 
eventually frees itself, and becoming detached, is lodged in 
the mantle chamber of the female Argonaut. This organ 
was for a long time a puzzle to naturalists, and has been 
described first as a parasitic worm, and then as the whole male 
Argonaut, and it is only of late years that its true nature 
has been made out. . 
Emhnjology. — Nothing whatever is known of the develop- 
ment of the Nautilus — According to Kolliker, in the Dibran- 
chiata the yolk division is onl}^ partial, the embrj^o is 
developed in a distinct germinal area, and a yolk-sac is 
formed, which is smaU in Argonauta, and large in Loligo and 
Sepia. The first process of development is the difierentiation 
of the embrj^o into mantle and foot, the latero posterior 
margins of the foot are produced into processes (4 or 5 on 
each side) which become arms, ridges develop upon the body, 
the posterior ends of which are free, but ultimately unite to 
form the funnel. Rudimentary gills appear between the 
funnel and the mantle. At first the alimentary canal is 
straight. "The embryo now grows faster in a vertical than in 
a longitudinal direction, so that it takes in the Cephalopodic 
form. The intestine as a consequence becomes bent upon 
itself, and the anterior pair of arms grow over in front of the 
