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. 



Eespiration 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 and 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 



