832 THE AMERICAN NATURALIST. [Vor. XXXV. 
finger-tips answering adequately for the purpose. Before the 
operation is completed, however, the siphuncular tube should 
be loosened ; this is effected by thrusting the hand within the 
shell below the siphon. At such treatment the animal retracts, 
but after several attempts the finger-tips find their way to the 
base of the siphuncle. In the inverted position the animal 
presents several peculiar features. The hood is bent and mis- 
shapen, and evidently possesses considerable plasticity. Adja- 
cent to it the black portion of the shell is largely exposed, 
owing to the retraction of the mantle. The tentacles are 
tumid, retracted, and are closely pressed together. The eyes 
stand out prominently, like mushrooms. The siphon shows 
its broad separation from the tentacular portion of the head, 
and hangs downward as a stout, muscular mass; at its base 
on either side droops a thin fold of the mantle (M A). |. Ot 
this the inky black edge corresponds to the black line already 
referred to as lying within the aperture of the shell. The 
entire mantle is now greatly retracted: its posterior ventral 
rim (M P) exposes a portion of the extensive mantle cavity, in 
which, although not shown in the figure, can be seen the gills. 
The animal while in this position is observed to give an occa- 
sional gasping movement which involves the adjacent mantle 
rim as well as the siphon folds; these are expanded and 
contracted quickly. 
The Tentacles and their. Movements, Extension and Retrac- 
tion. — Extension and retraction play an important and con- 
stant part in the economy of these organs. The maximum 
extension observed is about as shown in Fig. 8; shortly after 
death it is possible, however, to draw out the tentacles con- 
siderably further, to the degree which I have indicated in the 
swimming Nautilus of Fig. 1, or in the diagram, Fig. 13, C 
. Indeed, I suspect that the tentacles can be everted even fur- 
ther than this, should the animal be so disposed. It is of 
course doubtful if this protraction can be carried to the degree 
which would cause the obliteration of the distinct boundary 
line which separates the distal from the proximal portion of 
the tentacles. Judged from their varied movements, these 
organs have come to be highly specialized in the matter of 
