Nautilus.- 
-MOLr^USCA.- 
-Nauxilus. 
317 
Cultle-fishes. In addition to tLese there are four ocular 
tentacles, which Professor Owen imagines to he instru- 
ments of sensation, like the tentacles of the Dorides. 
The dorsal pair of the brachial tentacles are expanded, 
and unite to form a hood which closes the aperture of 
the shell, corresponding to the shell-secreting of the 
argonaut. This hood appears also to serve the animal 
as an organ of locomotion or kind of foot, analogous 
in action to the foot of the Gasteropods. The shell of 
the Nautilus is involute or discoidal, and consists of 
few whirls. Internally, it is divided into cells or 
chambers, by a series of partitions or septa^ and they 
are connected together by a tube or siphuncle. This 
siphuncle is membraneous, with a very thin nacreous 
investment, and is usually central. The last chamber 
is capacious, the cavity being twice as large as all the 
others put together. It is occupied by the animal, but 
the rest are empty, and are known as air chambers, and 
are lined by a very thin membrane. The use of th'ese 
air chambers appears to be to render the shell, with its 
inhabitant, of nearly the same specific gravity with the 
water. “ A Nautilus pompilius (in the cabinet of Mr. 
Morris),” sa 3 's Mr. Woodward, “ weighs one pound, and 
when the siphuncle is secured, it floats with a half 
pound weight in its aperture. The animal would have 
displaced two pints (two and a half pounds) of water, and 
therefore if it weighed three pounds, the specific gravity 
of the animal and shell would scarcely exceed that of 
salt water.” The object of the numerous partitions is 
probably more for the purpose of guarding against the 
collisions to which the shell is exposed, than for sus- 
taining the pressure of the water as has been surmised 
bj' some authors ; and the purpose of the siphuncle 
has been suggested bv Mr. Searles Wood to be that of 
maintaining the vitality of the shell during the long 
life these animals most likely enjoy. The sexes in the 
animals of this order are no doubt distinct, but all the 
specimens that have as yet been examined of the living 
Nautilus have been females. We are left to conjecture, 
therefore, how far the ditferences observable in the 
shells, and which have been made by conchologists of 
specific value, are dependent upon sex. Dr. Melville 
has been led to the conclusion from a study of these 
shells, that those individuals which are umbilicated are 
the males, and those without the umbilicus arc females. 
THE NAUTILUS POMPILIUS— fig. 211— is the only 
species the living inhabitant of which has been seen, 
and as these have all been females, and the shells are 
all imperforate, it has been suggested that the umbili- 
cated species, N. macromphalus, is the male. A 
wider range of observation, however, than can be easily 
obtained, would be requisite to enable us to pronounce 
with certainty on the subject. In a case so out of the 
reach of common observation, and in which so many 
circumstances concur to limit or baffle inquiry, it 
would be little in keeping with the spirit of science to 
give other than a probable opinion. 
Our knowledge of the habits of the Nautilus is very 
limited. Most probably, like the other cuttle-fishes, 
it feeds upon Crustacea and shell-fish. As we have 
mentioned before, the animals are not in the habit of 
swimming ; they creep upon the ground at the bottom 
of the sea. They are said, by means of their air 
chambers, to rise at will to the surface and sink aerain 
O 
on the approach of storms to the quiet recesses of the 
deep. They are also said to reside habitually at great 
depths in the ocean ; but as the partitions or septa 
appear to be formed periodically, and as the Nautilus 
must, consequently, have frequently an air cavity 
between it and the shell, it is evident that these 
chambered cephalopoda could not exist in very deep 
water. Empty bottles, we find, if securely corked, and 
sunk with weights beyond one hundred fathoms, are 
always crushed ; and therefore these shells with their 
Fig. 211. 
Nautilus Pompilius. Shell with animal. 
air chamoers, are probably limited to a depth of twenty 
or thirty fathoms at the utmost. The specimens which 
have been taken alive, have been captured at the 
surface ; and though they can undoubtedly swim by 
means of their respiratory jets, like other cuttle-fish, 
yet the form of their shell must be ill calculated for 
that method of progression. Their sphere of action is 
on the bed of the sea, where they creep like a snail, 
only mounting to the surface when driven up by storms. 
Rumphius was the first who described the animal of 
the Nautilus. “ When he floats on the water,” he says, 
“he puts out his head and all his barbs (tentacles), 
and spreads them upon the water, with the poop (of 
the shell) above water ; but at the bottom he creeps 
in the reverse position, with his boat above him, and 
with his head and barbs upon the ground, making a 
tolerably quick progress. He keeps himself chiefly 
upon the ground, creeping sometimes also into the nets 
of the fishermen; but after a storm, as the weather 
becomes calm, they are seen in troops floating on the 
water, being driven up by the agitation of the waves, 
whence one may infer, that they congregate in troops 
at the bottom. This sailing, however, is not of long 
continuance ; for having taken in all their tentacles 
they upset their boat, and so return to the bottom.” 
B 3 ’ what mechanism this ascent and descent of the 
Nautilus is effected is still a matter of conjecture. 
Professor Owen, whose “ Memoir upon the Pearly 
Nautilus,” is described by Dr. Johnston “as one of 
the best and most beautiful monographs in compara- 
tive anatomy,” thinks that nothing more is necessary 
