112 SEXUAL ORGANS. 



chiate Cephalopoda is undovibtedly that which relates to their 

 sexual union, accomplished through the offices of one of the 

 arms of the male, which becomes modified in its structure for 

 this purpose. This arm, very unlike the others in appearance, 

 sometimes becomes detached from the animal duf ing the sexvial 

 union, and remains within the mantle of the female for a period, 

 during which it enjoj^s a separate life. Each genus seems to be 

 characterized, not only by the particular arm, either on the right 

 or left side of the animal which is thus hectocotylized but also 

 by differences in its appearance and structure. The third left- 

 side arm of the Argonaut is first developed as a balloon-shaped 

 sack, which finally splits open and reunites its halves upon the 

 dorsal face of the arm which emerges from it, forming a chamber 

 which becomes filled with spermatophores, in a manner not yet 

 understood. Indeed the investigation of this whole subject may 

 be considered as yet in its infancy, and many points remain to 

 be cleared up ; thus in some genera no sack for the reception of 

 spermatophores has been found, aiid the hectocot3^1ized arm 

 appears to perform its office without subsequent detachment 

 from the animal, merely inserting itself within its own mantle to 

 gather spermatophores, which it proceeds to deposit upon the 

 buccal membrane of the female. The detached hectocotyle when 

 first discovered in the mantle of the female was naturally 

 regarded as a parasitic worm ; that of Argonauta being termed 

 Trichucephalus acetabularis by Chiaje and that of Octopus 

 Hectocotylus octopodin by Cuvier. More recently it was supposed 

 to be the entire male animal of the cephalopod. 



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 hectocot^dized arm, which at least occurs 

 usually in some genera, as four of them had 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. 



In Tremoctopus the third arm on the right side becomes 

 hectocotylized ; it is then worm-like in appearance, with two 

 rows of suckers on its ventral surface and an oval appendage at 

 the posterior end. The anterior part of the back is fringed with 

 a double series of branchial filaments (250 on each side). 

 Between the filaments are two rows of brown or violet spots. 

 The suckers (forty on each side) closely resemble, but are much 

 smaller than those of the normal arms. Between the suckers 

 are four or five series of pores, the openings of minute canals 

 passing into the interior. There is an artery and vein on each 

 side, giving branches to the branchial filaments, while a nerve 



