192 GENERAL ZOOLOGY 



lies within the outermost chamber of the shell and extends a 

 dorsal fold outward against the old part of the shell. When 

 the animal is contracted into the outer chamber a thick brown 

 hood conceals it from view. When the head is extended two 

 large eyes, about forty tentacles (arms), and a siphon are vis- 

 ible. The mouth is provided with a beak like that of the 

 squid, and with a rasping-tongue. Inside the mantle-cavity 

 there are four gills. There is no ink-sac. Another difference 

 between the chambered nautilus and the squid is the entire 

 absence in the former of the ability to change color. The 

 sexes are separate, as in the squid. 



The food of the animal consists of deep-water bivalves. In 

 obtaining food Nautilus probably uses the tentacles. Although 

 these organs have no sucking-disks, as the squid has, the 

 inner edges of the tentacles appear to have the power of flat- 

 tening against an object and of holding it effectively. 



Owing to the fact that Nautilus lives at great depths, we 

 know very little concerning its habits. Professor Willey, of 

 England, and Professor Dean, of Columbia University, have 

 studied the live Nautilus recently (1895 to 1901), and have 

 published reports on that subject. Nautilus is accustomed to 

 a great pressure of water and low temperature. When brought 

 to the surface in traps it could scarcely be expected to act 

 naturally. However, it seems reasonable to believe that the 

 method of locomotion would not be affected. It swims by 

 means of a jet of water from the siphon, and the convex sur- 

 face of the shell parts the water in its progress. 



Oliver Wendell Holmes, in his poem, The Chambered Nau- 

 ?, thus refers to the phenomena of its growth : 



Year after year beheld the silent toil 



That spread his lustrous coil ; 



Still, as the spiral grew, 

 He left the past year's dwelling for the new, 

 Stole with soft step its shining archway through, 



Built up its idle door, 

 Stretched in his last-found home and knew the old no more. 



