THE SLUG 



221 



in schools in our harbors and are often cast upon the shore after 

 a storm. They can also be obtained in the markets of our coast- 

 wise cities, since their flesh is used to 

 a certain extent as food. Cuttlefishes, 

 best known from their " bones " or rudi- 

 mentary shells lying deep in the mantle, 

 are inhabitants of deeper waters. They 

 have shorter bodies than the squids, 

 and their arms are eight in number, 

 instead of ten as in the case of the squids. 

 In both groups locomotion is effected bj' 

 the reaction to a stream of water which 

 is taken into the mantle chamber at the 

 edges of the mantle and is forced out 

 through the " funnel," which lies be- 

 tween the eyes (Fig. 212). 



The shell is rudimentary in both the 

 squids and the cuttlefishes, and like 

 that of the slug is embedded in the 

 mantle. There are two living genera 

 of Cephalopoda which have an external 

 shell. One is an ally of the cuttlefishes 

 — the paper nautilus or Argonauta,^ 

 which is found in all tropical seas. 

 The other is the sole survivor of a once abundant group. This 

 is the Pearl3^ Nautilus of the Indian and Pacific oceans. Its 

 shell is divided into water-tight compartments, in the last 

 formed of which the animal lies. It keeps its attachment to 

 the shell by means of a central strand of tissue — the siphon 

 (Fig. 213, s). Alhed to the Nautilus is the huge family of 



' A sailor in the Argo. 



Fig. 212 — Loligo Pealii, 

 Eastern squid. One-third 

 nat. size. FromRathbun. 



