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MANUAL OF ELEMENTARY ZOOLOGY 



four pairs of legs but has not yet reached the adult form. 

 During part of this stage the animal is quiescent. Demodex 

 folliculorum is a minute, long-bodied mite which lives in the 

 grease-secreting or " sebaceous " glands of the human face. 

 It is generally harmless, but appears sometimes to set up 

 skin disease and is accused of spreading the bacillus of 

 leprosy. In dogs it is the cause of a kind of mange. 

 Larva? and adults live in the glands and are transmitted by 

 contagion. Sarcoptes scabei causes the " itch " in man, and 



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Fig. 176. — The Sheep Tick (Ixodes ricinus). —After Nutlall. 

 A , Ventral view of male ; B, dorsal view of the same. 



a;,related species gives rise to mange in dogs. The adult 

 itch-parasite lives in burrows in the skin and there lays its 

 eggs. The larvae pass to the surface of the skin, where 

 they live, for the most part under the scabs which the 

 burrowing has caused to form, till the last stage, when the 

 female makes the burrow. The treatment consists in baths 

 and rubbing with various ointments, which generally contain 

 flowers of sulphur. Neither Demodex nor Sarcoptes possess 

 tracheae or eyes. The ticks, of which Ixodes may be 



