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 w T ell known, only a few specimens of the animal 

 have ever been obtained. 



2. Dibranchs. — These are the most active of Molhisks, 

 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 sw T im 

 backward or forward, usual- 

 ly with the back downward, 

 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 uatural size. Atlantic coasts. 



