ARGONAUTA ARGO AND THE IIECTOCOTYLI. 79 



account of the want of both the expanded arms and the shell. 

 But, in the first place, the similarity of the Hectocotylus-arm 

 with the free Hectocotylus speaks for that identity. Next, the 

 mode in which they occur : during a few days only did I obtain 

 the animals with the Hectocotylus-arm and Argonauts of the 

 ordinary kind in any quantity together. The latter were partly 

 larger ones with shells, partly also not more than 2-4 lines long, 

 and these, like the males, had no shell, at least as I obtained 

 them, while the expanded arms were already easily recognizable. 

 The colour and remaining form of the body were, however, in 

 such close agreement with those of the male animals *, that the 

 presence of the expanded arms and afterwards of the shell must 

 be considered not to be specific, but to be sexual differences. It 

 is perhaps not without importance, that these vela with a kind 

 of mesentery on the twisted axis of the arms occur in females 

 of that species whose males carry an arm so excessively deve- 

 loped, which however belongs to a different pair from the vela 

 of the female. The same probably holds good of Tremoctopus ; 

 for in this, as I shall elsewhere show, the two upper arms have 

 not the shape which is commonly figured, but form, when, as 

 rarely happens, they are well preserved, elongated lobes, which 

 excite as much surprise by their enormous size as by the extra- 

 ordinary magnificence of their coloration. 



It may be expected that the male Tremoctopus may have such 

 a structure, as to have been described as some other kind of 

 Octopus. Since Cuvier says nothing of any difference in those 

 Octopods which lodged the Hectocotyli from the other which 

 carried the Hectocotylus as an arm, it seems that the male, as 

 which the latter no less than Verany's specimen of Octopus Ca- 

 rena must be regarded, in this case is not strikingly different from 

 the female. 



3. The anatomical agreement of the suckers, &c. of each Hec- 

 tocotylus with those of the Cephalopod female upon which it 

 occurs, has been especially made out by Kolliker. 



4. In like manner the exclusive association of each Hectoco- 

 tylus with its kind of female only. Up to the present time free 

 Hectocotyli have only been found in the society of female Cepha- 



* Even the bundles of hairs described by Kolliker (Entwickelungsgeschichte 

 d. Cephalopoderi) were present as in the females of the size of a hazel-nut. In 

 larger specimens I no longer found them. 



