MOLLUSCS 



107 



enemies almost as 

 much as does its swift- 

 ness (Fig. 205). The 

 squid sometimes ap- 

 proaches a fish with 

 motion so slow as to be 

 imperceptible, and then 

 suddenly seizes it, and 

 quickly kills it by 

 biting it on the back be- 

 hind the head. 



i. s 



Fig. 206. — Pearly Nautilus. (Shell sawed 

 through to show chambers used when it was 



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

 tacles, T.) 



The octopus is more 

 sluggish than the squid. 

 Large species called 

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

 The pearly 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. 207.— Paper Argonaut (female). 



* Vi {i.e. the animal is three times as long 



and broad as figure) . 



Fig. 208. — Paper Argo- 

 naut (male), x %. 



General Questions. — The living parts of the mussel are 

 very soft, the name mollusca being derived from the 

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

 the molluscs, have the hardest coverings? 



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

 less) appropriate ? Lamellibranchiata (platelike gills)? 



