CEPHALOPODA 



85 



body is covered by the thick integument of the mantle. The internal 

 shell is calcareous and furnishes the cuttlebone used for canary birds. 



Cuttlefishes are carnivorous, feeding upon crabs, clams, or fishes. 

 They delight in the daylight and in the open sea, so they need to be pro- 

 tected from the view of their enemies. For this purpose they discharge 

 an inky fluid to cloud the water so as to escape detection. The dark- 

 colored secretion is carried in the ink-bag connected with the siphon. 

 The ink was used in ancient times as a writing fluid. The sepia ink used 

 by artists in making the sepia pictures is manufactured from this fluid of the 

 cuttlefish. The cuttlefish is also used as an article of food in the Old 

 World. 



Fig. 63. — Loli'go vulga'ris. (After Verany.) 



Squids (Fig. 63) swim in schools. They, unlike cuttlefishes, are noc- 

 turnal. They are carnivorous, feeding upon young fishes. The common 

 squid is a foot or less in length. The internal shell is a horny " pen " 

 shaped something like a feather, which is embedded in the dorsal portion 

 of the mantle. By alternately taking water into the mantle cavity and 

 forcing it out, the squid is driven rapidly backward. It avoids detection 

 by its color changes and by an inky discharge like that of the cuttlefishes. 

 It feeds upon small fishes and crabs, which it kills by biting with its power- 

 ful horny beak. Its enemies are large fishes and man. Giant squids are 

 over 9 feet long, with arms 20 or 30 feet in length. 



The octopus is another member of this class. It has a short subsi)herical 

 body without any shell. It has eight sucker-bearing arms, with which it 



