SEXUAL ORGANS. 



41 



quite distinct forms of cephaldpods, described as different 

 species ; this investigation is yet in its infancy, but will not 

 improbably result in a considerable reduction of the species, 

 man}- of which are already known to be insufficiently char- 

 acterized. 



The specialization of an arm for reproductive purposes in the 

 cephalopoda is curiously paralleled in the arachnida, as in some 

 species of spiders certain parts of the palpi of the males are 

 transformed for the same purpose into spoon-shaped organs. As 

 to the loss of the hectocotylized arm, which at least occurs 

 usually in some genera, as four of them have been discovered in 

 the mantle opening of a single female Octopus, there is no doubt 

 that another arm is developed to take its place, and it is 

 probable that these succeeding arms may be hectocotylized like 

 the first. 



We have already shown that in the male Nautilus the four 

 inner ventral tentacles become united into a so-called Spadix^ 

 which is now believed to perform in the tetrabranchiates the 

 office of a hectocotyle. 



\l. Steenstrup observes that it is evident this peculiar struc- 

 ture, sometimes of one pair of arms, sometimes of another, some- 

 times to the right, sometimes to the left, sometimes at the 

 summit", sometimes at the base, etc., must involve many differ- 

 ences in the mode of fixation of the spermatic masses or spermat- 

 ophores on the females, and (inasmuch as the semen does not 

 seem to be poured upon the eggs by involuntary or mechanical, 

 but by conscious movements) in the manner in which fecunda- 

 tion is effected. This is confirmed by observation. The sper- 

 matic masses are in reality fixed on very different places and in 

 very different conditions namely, in the genera Sepia, Sepio- 

 teuthis and Loligo (consequently all those in which he has found 

 the left ventral arm hectocotylized) the spermatic mass is fixed 

 on the internal surface of the buccal membrane of the females, 

 which is specially organized for that purpose ; whilst in the 

 other decapoda he has never found the sperms fixed in that place, 

 but on various parts of the mantle or of the interior organs, in 

 Ommastrephes, for example, far back in the cavity of the mantle, 

 towards the middle part of the back. 



