Iviii INTRODUCTION. [CH. 



sembles the pile of cloth, and is occasionally produced 

 into bristles or hairs ; but in most cases it is very thin 

 and only forms a delicate film. It exists also in shells 

 which are internal, as those ofLimax and Lamellaria, but 

 not in Cyprma or the cowry, which is constantly being 

 lubricated by the mantle. In its nature it appears to 

 be persistent and almost indestructible, being not unfre- 

 quently found still adhering to shells in upper tertiary 

 strata. 



CHAPTER IV. 



EXTERNAL RELATIONS. 



ENEMIES OF MOLLUSCA. PARASITES. USES TO MAN: VIZ. FOOD, 

 MEDICINE, ORNAMENT, AND ECONOMY. INJURIES TO MAN. 

 STUDY OF CONCHOLOGY. PLEASURES AND DRAWBACKS. INCI- 

 DENTS OF THE PURSUIT. 



Enemies of Mollusca. These soft creatures are the 

 favourite food of many animals. Man is not the only 

 one that finds them savoury and digestible, and that 

 hunts them down with insatiable voracity. The slow- 

 ness of their movements makes them an easy prey ; and 

 their shells afford them no protection against their 

 larger enemies. On land, hedgehogs (and it is said the 

 fox also), rats, thrushes, ducks and other birds, snakes, 

 lizards, toads, zoophagous beetles and centipedes pursue 

 them and greatly thin their numbers. An insect (the 

 Cochleoctonus vorax) lays an egg in the body of dif- 

 ferent species of snails, which, when hatched, eats up by 

 slow degrees the whole of its unwilling host, and then 

 curls itself up in the spire of the empty shell, until it is 

 turned into a chrysalis. The Mollusca which live in 

 fresh water are devoured by wild ducks and other birds 

 of that class, frogs, fishes, leeches, and the larvae of the 



