180 INTRODUCTION TO COXCHOLOGY. 



little worth ; yet the former^ during winter^ is nearly the 

 sole support of innumerable flocks of birds, and without 

 the latter a considerable proportion of the animal creation 

 would be entirely destitute of food. In the formation of 

 both, the Creator has deviated from his usual course, to pro- 

 vide for their security, and compensate for all their various 

 and necessary defects. 



A considerable number inhabit aquatic plants; others 

 are found on trees or slirubs ; and others in decayed wood. 

 They also abound in the most unfavourable and arid 

 situations. The few solitary vegetables which occasionally 

 diversify the extensive sands on the south side of the 

 Tagus, are incrusted with a species of small snail. Such 

 is also stated by African travellers to be the case in the 

 deserts of Sahara. 



The Helix pomatia, or Edible Snail, differs Uttle in appear- 

 ance from the common species. His tribe was introduced 

 into England by the celebrated Sir Kenelm Digby, as food 

 or medicine for his lady, when afflicted with consumption ; 

 and various attempts have been made to naturahze them in 

 Northamptonshire, but without success, as they uniformly 

 refuse to emigrate from the southern woods of England. 

 They are more susceptible of cold than their bretlii'en, and 



