;o 



MOLLUSC A. 



at both ends, with a foot greatly elongated and adapted 

 for boring in the sand, in which they live in from 60 to 

 600 feet of water on the sea-coast. The sexes are dis- 

 tinct. The young pass through several changes before 

 assuming the adult form. The shells form the wampum 

 of the Indians. 



Class IV. SQUIDS, etc. (Cephalopoda, head-footed). 



General Characteristics. The Cephalopods are the 

 highest forms of mollusks. They are marine, and either 

 swim or crawl ; have long arms or tentacles arranged 

 about the mouth, armed with suckers or hooks, two par- 

 rot-like beaks, and a toothed tongue. They generally 

 possess ink-bags; have highly developed eyes, and a large 

 brain protected by a cartilaginous covering, calling to 

 mind the cranium of vertebrates. 



Wing - footed Cephalopods (Pteropoda}. These, 

 the lowest and perhaps degenerate Cephalopods, are free- 

 swimmers, moving by two broad fins or wings upon each 

 side of the neck (Fig. 65, P). In Northern waters they are 

 found in vast swarms. The Cleodora emits a soft, clear, 

 phosphorescent light that gleams through the delicate shell. 

 The Clio, in swimming, almost touches its fins above and 

 below. It has a wonderful arrangement for seizing prey. 

 Each tentacle bears about 3,000 transparent cylinders, 

 each containing twenty stalked suckers ; and, as there are 

 six tentacles, the Clio can grasp its prey with 360,000 hands. 

 They have also a pair of many-toothed jaws, and a tongue 

 armed with recurved teeth a terrible array for so small a 

 creature. They are eaten by whales. The young pass 

 through several changes. 



Order I. Four-gilled Cephalopods (Tetrabranchi- 

 ata) ; Nautilus (Nautilida). Of 1,500 species that have 

 lived in past ages, only two are extant. The shell (Fig. 75) 

 is pearly, and divided into cells or rooms that are formed 



