V THE HECTOCOTYLUS ARM IN CEPHALOPODA I 37 



eiitly of the oviduct. Their purpose is to produce a viscid mucus, 

 which envelops the ova at the moment of their emission and 

 eventually hardens into the egg-capsules. A pair of accessory 

 nidamental glands occur in Sejna, as well as a pair of smaller 

 glands situated on the oviduct itself. 



In many of the male Cephalopoda the vas deferens is long 

 and dilated at its outer end into a glandular reservoir, within 

 which are formed the spermato]3hores, or narrow cylindrical 

 packets which contain a very large number of spermatozoa. 

 When charged, the spermatophores pass into what is known as 

 Needham's sac, where they remain until required for use. 

 These spermatophores are a very characteristic part of the 

 reproductive arrangements in the Cephalopoda. The male of 

 Sepia has been noticed to deposit them, during union, upon the 

 buccal membrane of the female. During the emission of the ova 

 by the female, the spermatophores, apparently through the 

 agency of a kind of spring contained at one end, burst, and 

 scatter the spermatozoa over the ova. 



The Hectocotylus Arm. — Perhaps the most remarkable 

 feature in the sexual relations of all the Mollusca is the so- 

 called hectocotylus of the Cephalopoda. In the great majority of 

 the male Cephalopoda, one of the ' arms,' which is modified for 

 the purpose in various ways and to a greater or less extent, be- 

 comes charged with spermatophores, and sometimes, during union, 

 becomes detached and remains within the mantle of the female, 

 preserving for some considerable time its power of movement. 



The hectocotylus is confined to the dibranchiate Cephalopoda, 

 and its typical form, i.e. when part of the arm becomes disengaged 

 and left with the female, occurs only in three genera of the 

 Octopodidae,viz. Argonciuta, Ocythoe {Philonexis), and Tremoctopus. 

 In all of these, the male is many sizes smaller than the female. 

 In ArgonautcL the third arm on the left side becomes hectocoty- 

 lised. At first it is entirely enveloped in a kind of cyst, in such 

 a way that only a small portion of the tip projects ; subsequently 

 the cyst parts asunder, and allows the arm to become expanded 

 to its full length, which considerably exceeds that of the other 

 arms. At a certain point the acetabula or suckers terminate, 

 and the remainder of the arm consists of a very long, tapering, 

 sometimes thread-like filament, which is pointed at the extreme 

 tip. It is not yet knowji how the spermatophores find their way 



