SEXUAL ORGANS. 113 



runs down the centre. The oval sack encloses a small but xqyj 

 long convoluted tube, ending in a muscular sack which contains 

 the spermatozoa. 



The hectocotyle of the Argonaut is ver}- small, onl}^ half an 

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

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

 but no branchiae. 



In Octopus the hectocotylized 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- 

 phores are probably transmitted to the terminal plate. 



It has already been shown that in the male Nautilus the four 

 inner ventral tentacles become united into a so-called Spadia?/ 

 this is now believed to perform in the tetrabranchiates the 

 sexual office. 



M. Steenstrup remarks that it is evident this peculiar structure, 

 sometimes of one pair of arms, sometimes of another, sometimes 

 to the right, sometimes to the left, sometimes at the summit, 

 sometimes at the base, etc., must involve many differences in 

 the mode of fixation of the spermatic masses or spermatophores 

 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 fecundation is 

 effected. This is confirmed by observation. The spermatic 

 masses are in realitj^ fixed on very different places and in very 

 different conditions — namely, in the genera Sepia, Sepioteuthis 

 and Loligo (consequentlj^ 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 A^arious 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. 



In the " Actes de la Societe Linneenne," of Bordeaux, 18Y2, 

 M. Lafont states that a Sepia Filliouxi deposited its eggs in one 

 of the basins of Arcachon, on the 23d of Maj^, 1810, attaching 

 them to a Zostera (xviii, 13-14.) Taking it from the water, 

 he found all around the mouth, attached \>j the large end, a 

 certain number of little sacs filled with spermatozoa. Replaced 

 in the water, the animal continued to oviposit. In again exam- 

 ining it, at the end of about a half-hour, he saw that the number 

 of sperm-sacks had diminished, not more than a dozen remaining. 

 As soon as again put in the water, a male approached and a 



