216 SNAILS AND SLUGS [CH. VII 



descend quickly through the air from trees and shrubs to 

 the ground or if necessary to perform the return journey. 

 During descent the slug travels head downwards, paying 

 out fresh mucus behind it, and gripping the cord with the 

 sides of the foot. The upward journey is of course a more 

 laborious task and is performed by bringing head and tail 

 together and transferring the point of attachment to the 

 former; the animal now travels head uppermost and the 

 gathered in cord is accumulated near the tail. In Limax 

 maximus, and some other species, pairing habitually takes 

 place in mid air ; the two individuals suspend themselves 

 head downward from some suitable object by a double cord 

 of mucus which supports their intertwined bodies. 



Food and Digestion. Plants form the chief food-supply 

 of terrestrial and fresh-water molluscs: indeed the mechani- 

 cal and chemical protective devices of wild plants seem to 

 be specially directed against the attacks of snails and 

 slugs. Tender succulent shoots and saccharine portions 

 of the plants are preferred and unerringly selected. Slugs 

 however are very general feeders ; some species of Lima- 

 cidce are omnivorous (I have seen a Limax' devouring 

 bird's droppings), others confine themselves to fungi ; all 

 are occasionally carnivorous, and some are predatory and 

 even cannibalistic; the species of Testacella habitually 

 devour earth-worms and other small animals. The food, 

 whatever its nature, is attacked by means of the radula 

 upon the floor and the hard crescentic chitinous jaw upon 

 the roof of the mouth. The radula 1 , or lingual ribbon, is a 



1 Geddes, Trans. Zool. Soc. Lond. x. Kossler, Zeit. wiss. Zool. XLI. 

 1885. Loisel, Journ. de VAnat. et Physiol. xxvm. Eiicker, Bericht, 22 d. 

 Oberh. Gesellsch. f. Natur, u. Heilkd. Giessen. 



