AttGONAUTA ARGO AND THE HECTOCOTYLI. 63 



appendage, in which it measured only '012 of a line; but 

 of its nature I can say nothing. The thickness of the whole 

 axis measured in one case at the end of the seminal capsule 

 0*39 of a line ; towards the end of the sucker-bearing portion 

 0-3 of a line; in the beginning of the appendage 0*15 of a Une ; at 

 the end of it 0*03 of a line. The inner tube measured at the 

 same points 0*24, 0*18, 0*08, and 0*025 of a line. 



The development of the Hectocotylus as an arm, while it ex- 

 plains the presence of a ganglionic chain, equally accounts for 

 the absence of any special organs of sense. But on this ground 

 the sensibility of the skin is very considerable. 



Since the muscular tube is filled by the chain of ganglia, the 

 supposition that an intestinal canal exists there, which Kolliker 

 himself considered doubtful, must be given up ; at least I have 

 perceived nothing of the kind. 



With respect to the circulation, I can unfortunately give no 

 information as to the connexion existing between the Hectoco- 

 tylus and the rest of the animal. In the separate Hectocotyli 

 the investigation is beset with difficulties, since they are for the 

 most part very restless, and wind and twist about in the most 

 determined manner. Yet a progressive wavy motion can readily 

 be observed in the trunks which lie upon each side of the back and 

 are immediately continued into the appendage. In one instance 

 I could distinctly perceive that this somewhat slow movement 

 passed upon the right side (the appendage being supposed to 

 be posterior and the suckers below) as far as the extreme point 

 of the appendage, and then returned in the opposite direction. 



After each wave towards the point, however, there succeeded 

 not merely a centripetal one upon the other side, but centri- 

 petal movements frequently arose, which commenced from the 

 point of the appendage. In other cases I met with a different 

 rhythm in the longitudinal trunks of the one and of the other 

 side, and a few times it appeared to me as if in the same vessel 

 the movement went on sometimes in one sometimes in the other 

 direction, as in the Tunicata. However, two vessels lying close 

 together might readily cause a deception in this case. 



Whether any distinct central organ of the circulation or heart 

 exist, I cannot as yet decide. 



There occur indeed considerable dilatations in the vessels; 



