

PHOTOGRAPH OF A MEDIAN SECTION THROUGH 

 THE SHELL OF THE PEARLY NAUTILUS 



It is only the large terminal chamber that is occupied by the 

 animal. 



PHOTOGRAPH OF THE ENTIRE SHELL OF THE 

 PEARLY NAUTILUS 



The headquarters of the Nautilus are in the Indian and Pa- 

 cific Oceans. They sometimes swim at the surface of the sea, 

 but they usually creep slowly about on the floor of compara- 

 tively shallow water. 



NAUTILUS 



A section through the Pearly Nautilus, Nautilus pompilius, 

 common from Malay to Fiji. The shell is often about 9 inches 

 long. The animal lives in the last chamber only, but a tube 

 (S) runs through the empty chambers, perforating the par- 

 titions (SE). The bulk of the animal is marked VM ; the eye 

 is shown at E ;-a hood is marked H ; round the mouth there are 

 numerous lobes (L) bearing protrusible tentacles, some of 

 which are shown. When the animal is swimming near the 

 surface the tentacles radiate out in all directions, and it has 

 been described as "a shell with something like a cauliflower 

 sticking out of it." The Pearly Nautilus is a good example 

 of a conservative type, for it began in the Triassic Era. But 

 the family of Nautiloids to which it belongs illustrates very 

 vividly what is meant by a dwindling race. The Nautiloids 

 began in the Cambrian, reached their golden age in the Silu- 

 rian , and began to decline markedly in the Carboniferous. 

 There are 2,500 extinct or fossil species of Nautiloids, and 

 only 4 living to-day. 



