ARACHNIDA. 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 ILI.—Acarvina. 
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 chelicerze and pedipalpi are used for piercing 
Fig. 182.—MITE CAUSING MANGE IN THE 
Pic (Sarcoptes scabit) x 120. 
Ventral view. Note the chelicerz, pedipalpi and four pairs of legs. 
