196 ZOOLOGY. 



(Fig. 127). The last is the case with the mites, iu 



which, therefore, the characters of segmented animals 

 can only be recognized in the 

 limbs. In the true spiders (Fig. 

 124) the body consists of cepha- 

 lothorax and abdomen. Arachnids 

 have always four pairs of legs, 

 which, in the true spiders, are 

 attached to the cephalothorax, in 

 the raites to the front part of 

 the unsegmented body. 



The chief Orders belonging 

 here are : (1) true Spiders (Ara- 

 FiG. 124— A Spider neldo) ; (2) Scorpions (Scorpio- 



CSaiHcusscenicus). nido) ; (3) Harvestmen (Opilio- 



nida) ; (4) Mites (Acaridea). Only the last contains 



species of importance agriculturally. 



Order : Acaridea (Mites). 



Small arachnids, in which the cephalothorax and 

 abdomen are fused together into one piece (Fig. 127). 

 The just-hatched young have three pairs of legs, the 

 adults, of course, four. 



Family : Acaridae (True Mites). 



Soft skin. No tracheae, no eyes. Legs short, often 

 with a sucker at the end. Here belong the Cheese 

 Mite (Acarus S'iro),the Meal Mite {TyroglyphusfariTwa), 

 and several other species living in dead organic sub- 

 stances; also — 



The Itch, or Mange Mites. 



These live as parasites on or in the epidermis, and 

 cause the itch or mange (scabies) in man, as well as in 

 several domestic animals. By means of the structure 

 and habits three genera are distinguished : — 



1. Digging, blood-sucking mange-mites living in 

 the skin (Sarcoptes) ; 



