SNAILS AND SLUGS. 247 



CLASS : CEPHALOPODA (CUTTLE-FISHES). 



The head is sharply marked off from the rest of 

 the body, and the mouth is surrounded by a circle 

 of arms bearing suckers or claw-like hooks. These 

 arms are supposed to be a modification of part of the 

 foot, the rest of this organ being constituted by a 

 hollow, funnel-shaped structure, which places the 

 mantle-cavity in communication with the exterior. 

 The water used for respiration is forced suddenly out 

 from the mantle-cavity, through the funnel, so as to 

 propel the animal in the opposite direction. A gland, 

 known as the "ink sac," secretes a brownish fluid, 

 which may be pressed out of the sac so as to shield 

 the animal from attack. All cephalopods are marine, 

 and, since they are therefore of no agricultural impor- 

 tance, it is unnecessary to enter into details regarding 

 their form and structure, and I will only mention the 

 following : Pearly Nautilus (Nautilus pompilius), with 

 external shell and numerous arms; Paper Nautilus 

 (Argonauta argo), with a very thin, boat-shaped shell, 

 and eight arms; Poulpe {Octopus), without shell, and 

 with eight arms ; Cuttle-fish {Sepia), and Squid {Loligo), 

 also without external shell, and possessing ten arms. 



CLASS: GASTROPODA (SNAILS AND SLUGS). 



Snails and slugs possess a head which bears un- 

 jointed tentacles, and also eyes, which, in many cases, 

 are borne on the tips of these. The foot serves for 

 creeping, and is flattened in a sole-like way on its 

 under side. The mantle is generally small, and limited 

 to the dorsal side of the animal. The usually spiral 

 shell covers therefore only a small part of the body, 

 but the rest of the body can also be mostly or entirely 

 drawn back into it. Snails possess jaws, but the 



