224 



PHYLUM ARTHROPODA 



caused by spirochaetes. The mites Demodex folliculorum (Fig. 159) 

 which lives in the sebaceous glands, and Sarcoptes scahiei 

 (Fig. 160), causing the itch, are ectoparasites of man which may 

 produce nothing more than irritation. 



Fig. 158. — The sheep tick {Ixodes ricinus) female, ventral surface on left, dorsal 



on right. 



A , anus ; G, genital aperture ; H, hypostome ; L.I, L.IV, first and fourth legs ; P, palp ; R, rostrum 



SH, oval shield ; ST, stigma.— After Wheler. 



'-^v^-' 



MM 



..' I. 





■"■/ 



• iV::V 



mm 



».:--.«..:^ 

 ^--'-.^ 



t--. ■ yi 



V. :.-.•> 



"«";.:;■•' 



Fig. i59._The Follicle 

 Mite (Demodex follicu- 

 lorum), in ventral view. 

 — From Thomson. 



Fig. 160.— The Itch Mite (Sarcoptes 

 scahiei), in dorsal view. The two 

 hinder pairs of legs are hidden 

 under the body. — From Thomson. 



