MOLLUSKS. 



321 



cling to rocks or retain its hold upon its prey. It has a 

 powerful parrot-like beak, with which it can crush the 

 shell-fish and the Crustacea that it captures. It can man- 

 age even a large Crab in this way. Winding its long 

 arms around it, and holding it, both body and claws, with 

 its numerous suckers, it deliberately crushes its various 

 parts with its strong mandibles, and picks out the flesh. 

 In the Indian seas this animal attains so large a size as to 

 be a dangerous enemy even to man. The color called 

 sepia comes from the Cuttle-fish. It is used by the ani- 

 mal for darkening the water with an inky cloud, that it 

 may more easily escape from a pursuing enemy. The 

 so-called cuttle-fish bone is a chalky substance secreted 

 from the mouth of the fish, and is composed of almost in- 

 numerable plates united by myriads of little pillars. 



553. The Argonaut, Fig. 253, called the Paper Nau- 

 tilus, from its thin, 

 white, delicate shell, 

 has, like the Cuttle- 

 fish, eight arms with 

 i uckers. Two of 

 these are expanded 

 into broad membra- 

 nous flaps. From ear- 

 ly times it has been 

 said that this animal 

 uses its membranous 

 arms for sails, and its 

 other arms for oars. 

 It has been found, 

 however, that the 

 membranes are not 

 used at all as sails, 

 but are usually spread 

 over the sides of the shell, meeting along its keel. It is 

 from them, and not from the surface of the body, that 

 the calcareous secretion is poured forth for the enlarge- 

 O 2 



Fig. 253 Argonaut, or Paper Nautilus. 



