596 



Slugs and Snails. 



[JAN., 



which acts as a rasping organ, that slugs and snails devour the 

 tissues of plants and other substances. Both the slug and snail 

 crawl upon a flattened portion of the body called the foot, 

 which, in the shell-bearing snail, can be retracted completely 

 into the shell. They breathe by means of the air coming in 

 contact with the highly vascular walls of a space in the body 

 known as the " mantle cavity." 



In both we find the male and female sexual organs in the 

 same individual — that is, they are hermaphrodite animals. They 

 do not, however, perform the act of self-fertilisation, except 

 under exceptional circumstances. Both slugs and snails copu- 

 late, the male and female sexual products ripening at different 

 times in the same individual. Both these molluscs deposit 

 eggs, which are large and very numerous. 



The slugs place their ova separately under the soil ; snails 

 usually in batches in slanting galleries in the earth, which are 

 formed by the parent snail. The eggs are round or oval, milky 

 white, semi-transparent bodies, and may be found under stones, 

 in damp moss, under boxes or any substances lying about upon 

 the ground, as well as in the earth. 



The slugs belong to the family Limacidce and the injurious 

 species to the three genera known as Avion, Limax, and Milar. 

 The first is distinguished by having a slime gland at the 

 posterior end of the body, and by having the respiratory open- 

 ing in front of the area over the rudimentary shell (the shield). 

 In Limax, the respiratory opening is at the back end of the 

 shield (Fig. i,f. x.). In Milax it is on the right side behind the 

 centre of the mantle, and the body is acutely keeled along the 

 back v Fig- h h. x.). 



The snails that are injurious belong to the family Helicidce and 

 to the genus Helix. Both slugs and snails are chiefly crepuscular, 

 or nocturnal, but many kinds will feed ravenously in the day- 

 time if the weather is damp, especially after heavy rains or 

 showers. Snails mostly shelter under leaves, stones, and in moss 

 during hot days ; most slugs prefer the earth for protection. 

 All snails seem to prefer green vegetation for food, but several 

 slugs have a decided objection to green plants and feed almost 

 exclusively on non-chlorophyllaceous matter, some preferring 

 dried vegetal products, others living on dead animal substances. 



