114 



Guide io Ai'achnida. 



Table-case 

 No. 26. 



Sub -ORDER VI.— VEEMIFOEMIA. 



The Acari belonging to this sub- order are degenerate, parasitic 

 forms "without tracheae, and with tlie posterior portion of the 

 body produced into an annulated caudal prolongation. The third, 

 fourth, fifth, and sixth pairs of appendages are short and three- 

 jointed. 



The sub-order includes the single family Dcmodicidac, the 

 members of which live in the sebaceous glands of the skin of man 

 and other mammals. A drawing of Demodcx caninus, a species 

 wdiich gives rise to follicular mange in dogs, is exhibited in Table- 

 case 26. This mite is about one-eightieth of an inch in size. 



Fig. 76. 



Dertwdex caninus, ven- 

 tral view of female. 

 Greatly magnifiecl 

 (after Canestrini). 



Fig. 77. 



Ventral view of a gall- 

 mite, Eriophyes sil- 

 vicola, X 135 (after 

 Canestrini). 



Sub-order VII.— TETEAPODA. 



These mites are degenerate forms, which resemble the Vermi- 

 formia in being without tracheae and in having the body prolonged 

 and annulated. The legs of the first two pairs are long and 

 provided with the normal number of segments, but those of the 

 third and fourth pairs are absent. 



To this sub-order belong the gall-mites, which form a single 

 family, Eriophyidae {Phytoptidae). They are of very small size and 

 are exclusively parasitic on plants of various kinds : many of them 

 give rise to pathological conditions resulting in scars, galls, or 



