MOLLUSKS 



IO7 



enemies almost as 

 much as its swiftness 

 (Fig. 205). The squid 

 sometimes approaches 

 a fish with motion so 

 slow as to be imper- 

 ceptible, and then sud- 

 denly seizes it, and 

 quickly kills it by bit- 

 ing it on the back be- 

 hind the head. 



The octopus is more 

 sluggish than the squid. 

 Large species called 

 devilfish sometimes have a spread of arms of twenty-five feet. 

 The pearlx nautilus (Fig. 206) and the female of the paper argo- 

 naut (Fig. 207) are examples of cephalopods that have shells. 

 The cuttlefish is closely related to the squid. 



Fig. 206. — Pearly Nautilus. (Shell sawed 

 through to show chambers used when it was 

 smaller, and siphuncle, S, connecting them. Ten- 

 tacles, T.) 



Fig. 207.— Paper Argonaut (female). 



x Vis {i.e. the animal is three times as long 



and broad as figure) . 



Fig. 208. — Paper Argo- 

 naut (male), x i/ 2 . 



General Questions. — The living parts of the mussel are 

 very soft, the name mollusca having been derived from 

 the Latin word mollis, soft. Why is it that the softest 

 animals, the mollusks, have the hardest coverings ? 



To which class of mollusks is the name acephala (head- 

 less) appropriate ? Lamellibranchiata (platelike gills) ? 



