SLUGS AND SNAILS. 299 



moving the broad growth of weeds and mud from the entrance 

 of pools where sheep may water, would do much good where 

 practicable. The destruction of the snails by putting gas-lime 

 or lime and strong salt over the mud when cleared out of the 

 dykes and ditches would greatly lessen the evil. 



In N. America L. humilis, and in S. America L. viator, 

 probably serve as hosts for the liver-fiuke. 



Slugs (LiMACiDiE) and Snails (HELiciDiE). 



Slugs and Snails are often a great pest to the farmer and 

 gardener. Now and then a plague of one or the other may 

 ruin our field-crops. These possess a head which bears ten- 

 tacles, and also a pair of eyes which may be on long stalks. 

 The foot is flat, and the rasping tongue or "radula" is well 

 developed. Both Snails and Slugs are hermaphrodites. The 

 eggs are laid in batches in the ground and under stones and 

 rubbish. 



The slugs have only a rudimentary shell or an indefinitely 

 formed one under the mantle. Slugs mostly frequent damp 

 places, and bury themselves during the daytime in the earth. 

 The eggs are laid singly, but in groups, in the ground, and are 

 very numerous. The chief genera are known as Arion, Limax, 

 and Agriolimax, Arion can be told by having the slime-gland 

 in the posterior extremity, and the respiratory orifice in front 

 of the shield-like shell. The Arions feed at night upon the 

 tenderest and choicest plants, but they will devour anything 

 at times. The Limaces are especially fond of indoor life. All 

 slugs excrete a thick slime, and this can be exuded at least 

 twice in rapid succession, a character which we may well 

 remember when we are trying to destroy them. 



The most destructive slugs are Agriolimax agrestis, L. maxi- 

 mus, Arion ater, and A. Tiortensis. 



The Greg Field-dug (A. agrestis) (fig. 174) is by far the most 

 injurious land mollusc. It may be found in most gardens and 



