PULMONIFERA ; SLUGS. 367 



the posterior part of the back, and frequently protected by a 

 shell. 



OKDER L PULMONIFERA. 



981. Although the greater part of 5he Mollusks of this 

 Order live on land, some are aquatic ; but these, like the aquatic 



FlG. 659. LIMAX RUFUS. 



air-breathing Insects and Vertebrata, are obliged to come occa- 

 sionally to the surface to breathe. They all feed upon vegetables, 

 and many of them do so exclusively ; but some are extremely 

 voracious, and will devour almost any organised matter that 

 falls in their way. They are diffused through all climates, 

 particular species being restricted to each. Those with a mi- 

 nute shell, usually concealed within the mantle, commonly 

 known as slugs, constitute the family LIMACID^E. In the com- 

 mon Slugs, as in most of' the terrestrial species of this Order, 

 we observe a prominent head, with four tentacula ; and at the 

 end of the longer pair the eyes are situated. These tentacula 

 can be drawn inwards by a process resembling the inversion of 

 the finger of a glove. On the back there is a kind of shield or 

 disk, formed by the mantle, which usually incloses a small shell. 

 This shield covers the pulmonary sac, the opening of which is 

 on the right side, and the head can be withdrawn beneath it. 

 The Testacella is a kind of slug which has the disc of the man- 

 tle at the posterior extremity, and this always contains a small 

 shell. This animal, which feeds largely on earth-worms, is 

 abundant in the south of France, and has lately been introduced 

 into the gardens of this country, where it is multiplying rapidly. 



