Ewing — Significance of Parasitism in Acarina. 43 

 psoROPTEs Gerv. 



p. equi (Herlng) — Equus caballus, E. asinus, E. caballuscfX E. asinusj. 



PSORALGES Trt. 



P. Uhertus Trt. — Tamandua tetradactyla (L.) and other species of tho 

 same genus. 



OTODECTEs Can. 

 0. cynotis (Hering) — Canis famillarls. Fells domestlca. 



In this family over forty species have been described. 

 Only eight of them have been recorded from more than 

 one host species, and they are found in seven of the nine 

 genera comprising the family. 



The study of the distribution according to host species 

 in these itch mites presents a puzzle indeed. Perhaps 

 no group of the parasitic Acarina has such a large per- 

 centage of forms restricted to a single host and yet, 

 strange to say, a few of the species have a distribution 

 among host species not closely related, for example Sar- 

 coptes caprae Flirstb. is found on man, the horse, and 

 several of the Bovidae. 



Several attempts at inoculation have been made by 

 other workers with various forms of itch mites, and 

 with results just as perplexing as the distribution of the 

 species themselves. 



I made a very careful attempt at inoculation with 

 Notoedres notoedres (Megn.) taken from rats, upon our 

 common striped ground squirrel, Spermophilus 13-lin- 

 eatus, but the attempt was a failure. Megnin was un- 

 able to get any successful inoculations with the Sar- 

 coptidae when placed on other than their normal hosts, 

 hence he called several of the forms, morphologically 

 identical, separate physiological species. Yet against 

 these experiments, it is established that the itch mite of 

 the dog, Sarcoptes canis, is transferable to man. 



