ARACHNID A. 



259 



they either hunt or catch by webs. One group, with 

 four pulmonary sacs, contains large hairy hunting spiders. 

 Some build small tunnels with trap-doors. The other 

 group, with only two pulmonary sacs, contains all the 

 common web-spiders. One species {Argyroneta) lives 

 under water in a web diving-bell. 



Female spiders, as a rule, are larger and more powerful 

 than males. 



Order III. — Acarina, 



The mites are small animals with soft globose body in 

 which there is no distinction of cephalothorax or abdomen, 

 and no trace of segmentation. They have four pairs of 

 legs and the chelicerse and pedipalpi are used for piercing 



Fig. 182. — Mite Causing Mange in the 

 Pig {Sarcoptes scabit) x 120. 



Ventral view. Note the chelicerae, pedipalpi and four pairs of legs. 



