SLUGS AND SNAILS. 51 



at least, in this yellow kind for there are 

 other sorts which have got rid of it alto- 

 gether. I am not sure that I have wounded 

 the poor thing very seriously ; for the shell 

 protects the heart and vital organs, and the 

 hoe has glanced off on striking it, so that 

 the mantle alone is injured, and that by no 

 means irrecoverably. Snail flesh heals fast, 

 and on the whole I shall be justified, I think, 

 in letting him go. But it is a very curious 

 thing that this slug should have a shell at 

 all ! Of course it is by descent a snail, and, 

 indeed, there are very few differences between 

 the two races except in the presence or ab- 

 sence of a house. 'You may trace a curiously 

 complete set of gradations between the per- 

 fect snail and the perfect slug in this respect ; 

 for all the intermediate forms still survive 

 with only an almost imperceptible gap between 

 each species and the next. Some kinds, 

 like the common brown garden snail, have 

 comparatively small bodies and big shells, so 

 that they can retire comfortably within them 



E 2 



