834 THE AMERICAN NATURALIST. (Vor. XXXV. 
of movement is exhibited which convinces the observer that 
under natural conditions Nautilus must be looked upon as an 
active form.! It will suddenly sweep from the bottom and 
bump its shell into a side or corner of the aquarium, — this, 
too, with considerable energy. At the shock the animal sinks to 
the bottom, partially retracts, and again remains almost motion- 
less. In these spasmodic movements the animal rarely rises 
more than three or four inches from the bottom, although on 
one occasion I observed it swim nearly to the surface, a ver- 
tical distance, however, of not more than forty-five cm. 
During the night-time the movements appear to be if any- 
thing less active than during the day. A curious rocking 
movement is often observed, the animal swinging forward or 
backward, or from side to side, but never to a degree suggest- 
ing a change in the resting position. Rotation — that is, turn- 
ing the shell to right or left — is very readily accomplished, 
and without, as far as I could see, any special movement on 
the part of the siphon. A very slight change in the direction 
of the water current exhaled from the siphon, aided by a slight 
leaning of the shell, is evidently enough to account for this 
ready movement, for the animal is delicately poised and little 
mechanical impulse is needed. Occasional distinct move- 
ments of the hood begin, and tentacles are observed. The 
hood. will partly close, then open again, somewhat abruptly. 
The tentacles show a peculiar weaving movement ; sometimes 
they separate quite widely from one another, and then 
converge. In their function as adhesive organs they will 
attach themselves somewhat delicately to objects presented to 
1 Professor Moseley, in his interesting Votes of a Naturalist on H. M.S. € 
lenger, observed that Nautilus swims with its tentacles “extended radially Hom 
the head, somewhat like the tentacles in a sea-anemone; but each pair has its 
definite and different direction, which is constantly maintained.” As far ves my 
own observations go, the exact position of the tentacles during swimming is not 
easy to determine, for the specimens were closely confined and their movements 
sudden and short; I am led to conclude, however, that the tentacles are drawn 
together during sustained movement, like those of other cephalopods. And 
this position I represented them, somewhat stiffly, perhaps, in Fig. 1. 
above volume, together with other references to Nautilus, I am indebted to. ud 
fessor Ijima, who kindly secured them for me in the University of Tokyo 
forwarded them to Misaki. 
