156 



MOLLUSCA 



Giant squids may reach a total length of thirty feet, the body being 

 not more than ten feet long. They form the food of the sperm 

 whales. Squids are used for bait and are eaten by French, Italians, 

 and the Orientals. Squid oil has been used for lubricating, and by 

 the Chinese as a medicine. 



The chambered nautilus {Nautilus pompilius) is a cephalopod 

 with a many-chambered, spiral shell, lined with beautiful pearly 

 nao'c. Unlike the squids and octopi, the nautilus lacks an ink sac 

 and cannot change its color. Oliver Wendell Holmes' celebrated 

 poem has immortalized " The Chambered Nautilus." 



The paper nautilus {Argo- 

 nauta argo) with a thin shell is 

 more active than the chambered 

 variety and is frequently seen 

 near the surface of the ocean. 

 The females are pelagic during 

 breeding season, but are found 

 in the depths the rest of the 

 time. The male Argonaut, one 

 inch long, only i/io of the size 

 of the female, has no shell, and 

 is able to detach the third arm 

 on the left side laden with sper- 

 matophores and spermatozoa. 

 The entire " hectocotylized 

 arm " passes into the mantle 

 cavity of the female and, at- 

 FiG. 7i5. Male Argonanta showing taching, permits the spermatozoa 

 hectocotylized arm. (Lull, Organic Evo- ^^ fertilize her eggs. (Figure 71, 



A and B.) 



Pearls. — Since so much of 

 the reputation for economic importance of the Mollusca depends 

 on the value of pearls, let us consider the source of pearls and 

 the methods used in producing " culture pearls." 



Composition. — The composition of pearls is 91.72 per cent 

 carbonate of lime, 5.94 per cent organic matter and 2.34 per cent 

 water. 



Source and Value. — The pearl " oyster," one of the Aviculidae, 

 Margaritifera, is not an oyster but a mussel. It is found in the 

 Persian Gulf and off the coasts of Ceylon and Japan. Similar forms 



lution, after Claus-Sedgwick. 

 of Macmillan and Co., Ltd.) 



Courtesy 



