NO. 418.] NOTES ON LIVING NAUTILUS. 833 
lengthening and shortening, if for no other purpose than that 
of their protection within the shell How these processes 
came to be evolved there is no good evidence for determining ; 
an aftractive hypothesis would connect them with the trans- 
verse foldings which permit the tentacles to serve as adhesive 
organs. And one can readily conceive that a 
process of shortening based upon the principle 
of transverse folds would result in the production 
of one highly effective fold, to the loss or detri- 
ment of the rest. This highly serviceable fold 
would of course be represented in the present 
boundary between the proximal and distal portions 
of the tentacle. According to such a view the 
proximal portion has now lost all traces of trans- 
verse segmentation, becoming, in fact, but a kind 
of sheath for the rest. The distal portion, on the 
other hand, on account of its varied move- B 
ments, has still retained them. It will 
accordingly be seen that the slender distal 
portion of the tentacle is not to be regarded 
as the homologue of a single highly A 
specialized sucking organ, as some 
writers have maintained. There is, 
I believe, no evidence that such 
sucking organs are to be looked for 
in the tetrabranch division of the 
cephalopods. On the contrary, this 
division, possessing tentacles many 
Pit pans cont soscd any Ce 
; y have 
required the specialized sucking rings which characterize the 
few-armed cephalopods. à 
: The Movements of Nautilus. — In captivity Nautilus remains 
in one position, sometimes for hours. This sluggishness, how: 
ever, may reasonably be due to the shock it suffers in being 
suddenly brought to live in surface water. Slight movements 
of the ends of the tentacles are sometimes the only signs that 
the animal is still alive. Spasmodically, however, a strength 
A 
