10 STUDIES ON ACAEL 



foUiculonim (= D. folliculorum) appeared in 1844, and is still of 

 considerable value, for although the figures are faulty in detail, they 

 give a good idea of the proportions of the various stages of this mite. 

 Leydig's fine paper on Demodicidse and Sarcoptidoe was published in 

 1859, and contains the descriptions oi D. phi/llosfomatis, D. canis, and 

 D, hominis {=^ B. folliculorum). In 1877 and 1880 Megnin published 

 his observations on the family, dealing with D. folliculorum var. caninus 

 {= D. canis), var. hominis {=■ folliculorum), and var. catti (catti), 

 giving many valuable details of structure, accompanied by accurate 

 measurements and figures. The Demodex of the pig {D. phjlloides) 

 was found by Csokor in 1879, and his descriptions of the group and 

 species are very interesting and of quite exceptional merit. In his 

 'Traite de Zoologie Mcdicale et Agricole ' (2nd edition, 1895), 

 Kailliet gives a short resume of the family Demodicidse and lists 

 the known species, giving names to the Demodex of the horse, 

 goat, and sheep. The discovery of the Demodex of the mouse is due to 

 Oudemans of Arnhem (1897), who discusses the affinities of the group, 

 pointing out the striking resemblance to Psorergates of the family 

 Cheletidae. The account of the family Demodicidae by Canestrini in 

 the ' Tierreich ' is very poor and incomplete, but- he gives a good 

 description of the group and deals especially with D. folliculorum, 

 D. caninus (:= D. canis), and D.bovis in his ' Prospetto dell' Acarofauna 

 Italiana' (published in 1899). Professor Domenico Majocchi, of 

 Bologna, fully discusses the relations of D. folliculorum with various 

 skin-diseases in several elaborate and well illustrated papers (1879- 

 1914). Finally, we have the masterly papers written by Gmeiner 

 (1908 & 1909) giving a list of the known species, with good 

 measurements, etc., copious literature, and a long list of experiments 

 dealing with the effect of various chemicals (especially the etherial 

 oils) on Demodex. 



THE OEIGIN AND AFFINITES OF THE GEOUP. 



The mites of the family Demodicidse are regarded by most acarologists 

 as au isolated group, and owing to the extreme, often vermiform 

 elongation of the body and annulation of the abdomen, they are 

 sometimes placed in the same suborder as the Tetrapoda (Eriophyidse) 

 a family also exhibiting these peculiarities but otherwise very dissimilar 

 in structure. Oudemans has hinted at their derivation from the 

 Sarcoptidae (Astigmata) parasitic in mammals, and has also drawn 



