ARACHNIDA. 297 



races ; waging unceasing and merciless warfare against 

 them ; some attach themselves to the bodies of various 

 animals, and extract their juices through the skin : 

 while a very few seem to live on vegetable substances. 

 The Class is divided into two Orders, distinguished 

 by a variation in the mode of respiration. The first, 

 which is by far the more numerous, displays more 

 fully the peculiar organization of the Class ; the 

 other approaching in many respects, the true Insects. 



