54 MULLER ON THE MALE OP 



two upper and the two lower arms were longer than the lateral 

 ones ; of the latter on the right side three only were present ; 

 while on the left side there existed, in all the specimens which 

 I received, in the place of the lower lateral arm, the sac in 

 question, supported by a short and delicate pedicle, as if it were 

 constricted. The pedicle arose from a small depression between 

 the second and fourth arms and the mouth, from which the sac 

 could be easily drawn out a little. The membrane which unites 

 the base of the arms of the Argonaut passed upon the left side 

 from the second to the fourth arm, without immediately invest- 

 ing the sac, whose position was somewhat internal to it. 



The sac itself was not so long as the arms in the smallest 

 specimens, whilst in the larger it equalled or exceeded them in 

 length. In shape it was not exactly round, but somewhat 

 elongated and compressed in such a manner that the diameter 

 in a radial direction from the mouth was greater than in the line 

 of the two neighbouring arms. The colour, like that of the rest of 

 the body, was intensely reddish brown when the chromatophora 

 were dilated, more greyish when they were contracted. Only 

 on the inner, oral side was there a white streak without chro- 

 matophora, which however did not extend over the whole length 

 of the sac. 



In all cases a Hectocotylus Argonauts lay coiled up within the 

 sac. It was curved towards the side which bears the suckers, so 

 that the back of the thick part corresponded longitudinally with 

 the internal convexity of the sac. The part described by Kol- 

 liker as a silvery sac, forms at this place, immediately under the 

 skin of the sac in large specimens, a ridge-like elevation visible 

 externally, through which a whitish tint often glistens. The 

 thinner part of the sucker-bearing body is bent back along the 

 inner convexity of the sac towards the base, and the filiform ap- 

 pendage lies between them in multitudinous convolutions. 



This position of the Hectocotylus is frequently obvious from 

 without, especially during the lively movements which it often 

 makes ; and still more clearly on the opening of the sac, when 

 it uncoils itself from its narrow cell under the eye of the spectator. 



The relation of the Hectocotylus to the capsule in which it lies, 

 and the change which the latter undergoes after its eversion, 

 are very remarkable. 



