90 ANIMAL FORMS 
in the nautilus it is coiled and of considerable size, and, un- 
like that of any other cephalopod, it is carried on the out- 
side of the animal. Interiorly it is divided by a number of 
partitions into chambers, the last one of which is occupied 
by the animal. 
The alimentary canal shows some resemblance to that 
of other mollusks, but, as in the case of the other systems 
of the body, it possesses a far higher state of development. 
The mouth is situated in the center of a circle of arms, 
which in reality are modified portions of the foot, and is 
furnished with two parrot-like jaws. From this point the 
esophagus leads back into the body mass to the stomach, 
which with the liver and intestine are sufficiently like 
those of the clam and snail to require no further comment. 
Respiration is effected by the skin to a certain extent, 
but chiefly by two gills (four in the nautilus), and the cir- 
culatory system, which conveys the blood to and from these 
organs and over the body with its complex heart, arteries, 
capillaries, and veins, is more highly developed than in 
any other invertebrate. 
As might be expected in animals with so great sagacity 
and cunning, the nervous system of the sense-organs reach 
a degree of development but little short of what we find in 
some of the vertebrates. The chief part of the nervous 
system is located in the head, protected by a cartilaginous 
skull, a very rare structure among invertebrates; and while 
the different ganglia may be recognized in a general way 
and be found to correspond to a certain extent to those 
of foregoing mollusks, they are so largely developed and 
massed together that it is impossible at present to under- 
stand them fully. From this point nerves pass to all 
regions of the body, to the powerful muscles, the viscera, 
and the organs of special sense, controlling the complex 
mechanism in all its workings. 
There is no doubt that the cephalopods see distinctly 
for considerable distances, and a careful examination of 
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