40 8EXIAL OUGAXS. 



speriii;ilo[)liores has l>eon t'omid, aiul the licctoeotylized arm 

 appears to perform its otliei' without siil)s('([iu'nt detachment from 

 the .aniJiial. The detached hectocotylc when first discovered in 

 the mantle of tlie female was naturally regarded as a parasitic 

 worm: that of Argonauta being termed IVichocephalus acelobn- 

 larii< by Chiaje and that of Octopus Hectocotylu}> ocfopodis by 

 Cuvier. More recently it was supposed to be the entire male 

 animal of the cephalopod. 



In Treinoctopns the third arm on the right side becomes hee- 

 tocotylized ; 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 i)art 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, l)ut are much smaller than 

 those of the normal arms. Between tlu' 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 runs down the 

 centre. The oral sack encloses a small but very long convoluted 

 tube, ending in a muscular sack wiiich contains the spermat(;zoa. 



The hectocotyle of the Argonaut is very small, only half an 

 inch, with a filiform appendage in front of about eijnal length ; 

 it has two rows of alternate suckers, forty-five on either side ; 

 but no branchise. 



The Father of Natural History, who was certainly a first-class 

 observer, was acquainted with the hectocotylized arm and its 

 functions, but his degenerate successors for man^- centuries not 

 only misunderstood if but him also. 



In Octopus the liectoc€)tylized arm instead of being much 

 shorter than the others, as in Argonauta, becomes much longer. 

 It terminates in an oval plate, marked with numerous transverse 

 ridges and intervening pits, and this is connected by a muscular 

 fold of skin running along the dorsal face of the arm with the 

 webbed base, covering a passage through which the spermato- 

 |)hores are probably transmitted to the terminal plate. 



It will be seen in the systematic jyortion of this work that able 

 observers have in some cases regarded as op[)Osite sexes only 



