158 SEA-SHORE LIFE 
belief it never swims at the surface. The chambers of the shell, 
the construction of which we have already mentioned, are filled 
with gas, this being a mixture of oxygen and nitrogen resemb- 
ling ordinary air, but being richer in nitrogen. This gas prob- 
ably serves to increase the buoyancy of the shell, so as to 
enable the animal to move more rapidly. The animal itself is 
confined to the outermost and largest chamber of the shell. The 
mouth is provided with a pair of parrot-like beaks composed of a 
black, horny substance, coated on the outside with shelly matter. 
There are about 90 tentacles around the mouth. ‘These have poorly 
developed suckers, and can be retracted each into its own special 
sheath. The sheaths of two of these tentacles are fused into a 
broad, flat plate called the hood, that serves to partially close the 
aperture of the shell when the animal retracts. This hood les on 
the back of the head, while on the lower side we find a tube made 
of two side folds which overlap. This is the “siphon” or fun- 
nel through which water is expelled, driving the animal back- 
ward. In this manner it swims through the water near the bottom, 
gliding along with the aperture of the shell turned upwards and 
the tentacles held close together and trailing out horizontally. The 
writer was informed by natives of the Paumotu Islands, however, 
that the nautilus also crawls over the bottom, and often buries itself 
beneath the sand. 
In the Philippine Islands the nautilus is captured in traps 
somewhat similar in construction to our lobster-pots, the bait used 
being pieces of chicken or even dead dogs and cats. The animal 
is eaten in these islands but is not highly esteemed, and a better 
price is now obtained for the shell, which is used in China for the 
manufacture of pearl buttons. 
The tentacles and funnel-tube are opaque-white, while the 
hood is speckled with brown and yellow spots. There is a simple, 
pit-like eye mounted on a short stalk on either side of the head, and 
this is so placed that it can obtain a view of the surroundings even 
when the creature is almost completely retracted, and the aperture 
of the shell all but closed by the hood. The shell of the nautilus 
is smooth and white and marked with bands of reddish-brown, 
while the inner side of the aperture is marked with jet-black where 
the mantle fold is applied to the shell. The partitions of the cham- 
