182 GENERAL ZOOLOGY 



animal withdraws into its shell, allowing the edge to fit 

 closely to the object. Then certain glands in the collar 

 secrete mucus, which flows from all sides over the under 

 surface of the foot, between it and the supporting surface. 



When the membrane dries it has the appearance of stiff, 

 oiled paper of considerable toughness. It is called the epi- 

 phragin. It is supposed that the epiphragin aids in retaining 

 the body-heat during the four to six months of sleep. Metab- 

 olism (see p. 206) continues through all that time, but at a 

 much reduced rate. A very small hole is to be found in the 

 epiphragin, in one species of Helix at least, just below the 

 lung-aperture. Through this oxygen and carbon dioxide may 

 continue to pass. With the returning warmth of spring the 

 snail bursts the epiphragm and recommences active life. 



The Garden-Slug. The particular species of garden-slug, 

 the habits of which are suggested in Fig. 94, is Li'max 

 max'imus. It is a native of Europe, not of America, and 

 since its introduction here has become a more unwelcome 

 guest in greenhouses than any other species of slug or snail. 

 As yet it is not widely distributed from the vicinity of 

 New York and Boston. 



In brief terms we may describe a slug as a snail with a 

 rudimentary shell. The elliptical plate of muscle on the 

 dorsal surface of Limax is all that is left of the mantle. In 

 the process of degeneration, which we may well suppose has 

 occupied thousands of years, the mantle folded back over 

 the shell as the latter decreased in size. If we examine the 

 interior of the mantle, we find a thin, calcareous plate, which 

 is undoubtedly the rudimentary shell. 



Aside from the difference in the size and form of the shell, 

 Limax maximus and Helix nebulosa are very much alike. 

 The body of Limax is straightened out, but the organs which 

 in Helix have openings on the right side of the body also 

 have openings on the right side in Limax. These are the 



