280 



COMPARATIVE ZOOLOGY. 



straggler of a mighty race dwells in the deep parts of the 

 Indian Ocean, crawling on the bottom ; and, while the 

 shell is well known, only a few specimens of the animal 

 have ever been obtained. 



2. Dibranchs. These are the most active of Mollusks, 

 and the tyrants of the lower tribes. Among them are 

 the largest of invertebrate animals. They are naked, hav- 

 ing no external shell covering the body, but usually a 

 horny or calcareous part within. They have a distinct 



head, prominent eyes, horny 

 mandibles, eight or ten arms 

 furnished with suckers, two 

 gills, a complete tubular fun- 

 nel, and an ink-bag contain- 

 ing a peculiar fluid (sepia), of 

 intense blackness, with which 

 the water is darkened to fa- 

 cilitate escape. They have 

 the power of changing color, 

 like the Chameleon. They 

 crawl with their arms on 

 the bottom of the sea, head 

 downward, and also swim 

 backward or forward, usual- 

 ly with the back do wnward, 

 by means of fins, or squirt 

 themselves backward by forc- 

 ing water forward through 

 their breathing funnels. 



The Paper Nautilus (Ar- 

 gonauta) and the Poulpe (Octopus) have eight arms. The 

 female Argonaut secretes a thin, unchambered shell for 

 carrying its eggs. The Squid (Loligo) and Cuttle-fish 

 (Sepia) have ten arms, the additional pair being much 

 longer than the others. Their eyes are movable, while 



FIG. 248. Cuttle-fish (Sepia officinalis) 

 one fifth natural size. Atlantic coasts. 



