1 905.] 



Slugs and Snails. 



595 



The common field slugs are practically omnivorous, but others 

 prefer certain kinds of food, though they will devour almost 

 anything under stress of circumstances. Unlike a snail, a 

 slug has no external shell, except in one genus ( Testacelld) ; the 

 shell is present, however, as a small flat plate, sometimes almost 

 only a mass of granules, hidden just under the skin. Their soft 

 body is extremely contractile, and the moist skin is provided 

 with numerous glands which secrete a slime which can be passed 

 out very copiously for a short time. The slime glands soon get 

 exhausted, and take some time to regain their energy. The 

 slug has a distinct head with contractile tentacles, upon the ex- 



Fig. I. — Characters of Slugs.— a. Eggs; b. Shell of Slug (Limax) ; c. Shells 

 of Testacella ; d. Grey Field Slug (Limax agrestis) ; e. Shield showing respiratory 

 pore (x) of an Arion ; f. of a Limax ; g. Tail end of a Testacella showing shell (z)j 

 h. Shield showing respiratory pore {x) of ,Milax. 



tremities of which are placed the eyes. The mouth, as in the 

 snail, is provided with fleshy lips, and within is placed a long y 

 ribbon-like body, called the radula. This radula is provided 

 with transverse rows of teeth, which differ in form and arrange- 

 ment in different mollusca. It is by means of this structure, 



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