Etiology. 



9B3 



which are placed on long pedicles with three joints, while the third pair of feet in 

 the female terminates in two long bristles; in the male on the posterior edge of the 

 body there are two prolongations, and on the abdominal side two tumbler shaped 

 suckers which in copulation take up the two generative appendages of the female 

 (Fig. 140). 



To this class belong: 



(a) Dermatocoptes communis; in the horse, cow, buffalo and sheep. 



(b) Dermatocoptes cunieuli; parasitic in the external auditory canal of the 

 rabbit. 



The dermatocoptes mites bore through the epidermis layer with their jawa 

 and rostrum as far as the cutis, in order to suck up fluid (hence often colored red) ; 

 they do not penetrate into the epidermis layer but remain on the surface of the 

 skin, between and under the encrustations. 



3. Dermatophagus (Chorioptes, Symbiotes, scale-eating mite) ; is 0.3 to 0.4 

 mm. long, its size is midway between that of the two previously described mites; 

 the body is elongated, oval, the head blunt, shorter than broad, bluntly conical; the 

 blunt wedge-shaped lower jaws are only suitable for crushing substances which are 

 taken up; the suckers are goblet shaped, on short non-jointed pedicles; in the 

 female they are found on the first two and on the posterior pair of legs, while the 



140. Dermatocoptes communis v. equi. On the right, female, viewed from above 

 On the left, male, abdominal view. Magnif. 75. (After Megnin.) 



third i)air end in long spines; in the male there are suckers on all four pairs of legs, 

 the last pair is, however, generally rudimentary; the genital plugs or processes are 

 similar to those of dermatocoptes, only with the difference that the plug shaped clasp- 

 ing organ of the male D. communis besides the roundish bristles, bears also a rather 

 long bristle, like a blade of grass and slightly twisted. 

 To this variety belong: 



(a) Dermatophagus communis; in horses, oxen and sheep. 



(b) Dermatophagus auricularis (Symbiotes eeaudatus) ; resii!os in the ex- 

 ternal auditory meatus of dogs, cats and rabbits (Fig. 141). 



The masticatory apparatus of the dermatophagus mite pernits them to feed 

 only on the crusts and epidermis scales of the inflamed skin, but no: to bore thi'ough 

 or dig into the skin. 



Besides the enumerated varieties, sub-varieties may occur according to the 

 species of animal on which the mites become parasitic (Sarcoptcs scabiei var. equi, 

 ovis, capra% suis, etc.) ; this far-reaching division originated on the one hand through 

 the frequent non-success of transmission, and on the other is founded on differences 

 in size, which, however, probably also depend on the special peculiarities of the body 

 of the host (thickness of skin, hairiness, etc.). 



