102 PARASITES OF THE DOMESTIC ANIMALS 



concealed beneath the abdominal margin when the acarus is in dorsal 

 view. In the female the first two pairs of legs are terminated by stalked 

 ambulatory suckers; the posterior pairs by bristles. In the male all 

 of the legs are provided with stalked suckers but the third pair which 

 terminates in bristles. The anus is located upon the posterior dorsal 

 margin of the abdomen. Just anterior to this in the female is the copu- 

 lating vagina (receptaculum seminis). Upon the ventral side at the 

 median anterior border of the abdomen of the ovigerous female is the 

 genital pore. The males have no copulatory suckers or abdominal ex- 

 tensions. 



The Sarcoptes live upon man and practically all of the domestic 

 manuTials. In the latter animals they seek the parts of the body where 

 the hair is short, while in man their preference is for places where the 

 skin is thin, as about the knuckles, between the fingers, and in the bend 

 of the elbows and knees. A peculiarity of their attack is the habit in 

 the female of cutting timnels beneath the epidermis, in the bottom of 

 which she deposits her eggs (Fig. 65), a circumstance that renders this 

 form of acariasis relatively difficult to cure. 



The Sarcoptes inhabiting the skin of various animals cannot be said 

 t o exhibit differences of specific importance. They may, therefore, be 

 placed in a single species — Sarcoptes scabiei — which may give rise to 

 varieties according to host, as Sarcoptes scahiei, var. hominis of man, var. 

 equi of the horse, and var. suis of swine, etc. The slight difference in 

 these, as in other Sarcoptidae, is mainly one of size. 



Psoroptes (Figs. 68 and 69). Sarcoptidae (p. 101). — The body is 

 oval, the mouth parts elongated and in the form of a cone. The legs 

 of the anterior pairs are thick, the posterior pairs more slender; all four 

 pairs extend beyond the margin of the body. In the female the first 

 two pairs of legs and the fourth pair are terminated by ambulatory 

 suckers carried on long, three-segmented stalks, the third pair being 

 terminated by bristles. The male has copulatory suckers serving for 

 fixation to the female, and short posterior abdominal prolongations 

 terminated by bristles. The first three pairs of legs are terminated by 

 stalked suckers; the fourth pair is stunted. 



Psoroptic scabies, the form produced by the members of this genus, 

 is the most common and has been longest known. Unlike Sarcoptes, 

 Psoroptes seek the parts of the body where the hair is long; they do not 

 burrow beneath the epidermis, but attack the skin upon its surface, 

 ' their punctures being followed by the formation of thick crusts. Under 

 these they live in colonies which may coalesce and eventually cover 

 areas of the body more or less circumscribed. Psoroptic scabies is most 

 often observed upon animals with bodies covered wholly or in part by 

 long hair, as the sheep, ox, and horse. 



As with Sarcoptes, the difference in host inhabited by Psoroptes 



