ARGONAUTA ARGO AND THE HECTOCOTYLI. 71 



the Hectocolylus Tremoctopodis is analogous to the filiform ap- 

 pendage of Hectocotylus Argonaut. 



Of the six specimens in which the cleft in the capsule was 

 open, three were particularly distinguished by having no penis 

 visible externally. It was not torn off, as might have been con- 

 cluded from the absence of the opening out of which it generally 

 passes * ; but it lay spirally coiled up under the skin inferiorly 

 behind the last suckers, and, indeed, more towards the right 

 side. It was very short, but relatively thick. Here then it was 

 clearly evident that the penis is the immediate continuation of 

 the muscular axis, which could not be so well demonstrated in 

 specimens with a long free penis. Close behind the last suckers, 

 the end of the thick part of the axis, which contains the last 

 ganglion, lies in such a manner in the lower wall of the capsule, 

 that it can be seen through the dorsal cleft above mentioned as 

 a knob somewhat projecting from the inner surface of the cap- 

 sule. From this the muscular tube bends down to the lower 

 side of the Hectocotylus and forms the penis, which here lies 

 coiled up under the skin, instead of as usual passing forward 

 and becoming free in the neighbourhood of the third to the fifth 

 sucker. 



Where the axis bends down, the longitudinal vascular trunks 

 pass into the penis f Immediately beyond this flexure the. 

 ductus deferens, generally convoluted, comes from the left side 

 to the anterior side of the penis into which it penetrates. The 

 larger convolutions which this duct frequently makes at the 

 base of the penis produce the transverse ridge, which may be 

 frequently observed in many Hectocotyli between the body and 

 the capsule upon the lower side. 



If now we consider the place of the cleft capsule, keeping in 

 mind this relation of the penis to the axis, its position upon the 

 back of the axis (where the thicker part passes into the thinner) 

 is quite analogous to that of the membranous lobe in Hectoco- 

 tylus Argonautce. 



* In one specimen the semicircular edge which usually surrounds the aper- 

 ture behind was faintly indicated, perhaps in preparation for the subsequent 

 exit. 



f Whether at an earlier period the contents of the axis also are continued 

 into the penis, I cannot decidedly say. 



