CHAPTER VII. 



DISPERSAL OF SLUGS. 



Slugs, obviously, are not so well fitted for dispersal as 

 snails, for many are quite naked, and though some 

 possess small external shells, the well-developed snail- 

 shell, into which the animal can retire for rest and 

 during periods of adversity, and which, often closable 

 by an epiphragm or operculum, has doubtless largely 

 facilitated the dispersal of shell-bearing kinds, is always 

 absent, and it is clear, therefore, that many of the con- 

 siderations referred to in the preceding chapter cannot 

 be looked upon as necessarily applicable to the slugs, 

 such creatures being sure to succumb to many of the 

 hardships from which snails may often have escaped in 

 safety. Many slugs, it is notorious, from containing 

 much water, cannot even bear exposure in a dry at- 

 mosphere for any length of time, but in many respects, 

 it should be remembered, animals of this kind are much 

 more tenacious of life than might at first be supposed, 

 and this is true of our ordinary absolutely naked sorts, 

 Umax, Avion, etc. The Testacellce, which have a small 

 ear-shaped shell near the extremity of their bodies, 

 *' snail-slugs " of some authors, are able to protect them- 



