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and short, of three joints, but the basal is usually united to the 

 rostrum. There are no spiracles, and respiration is therefore through 

 the general surface of the skin. The sexes are often quite different 

 in structure. The females usually deposit eggs, the larvae are hexo- 

 pod, and there are two nymphal stages. They are all parasites, 

 mostly on mammals and birds, and often burrow in the skin, causing 

 mange, or scabies. 



Only one species has been taken on rats; this belongs to the genus 

 Notoedres. 



Notoedres. In this genus the third pair of legs of the male and 

 the third and fourth of the female have no sucker at the tip. The 

 anal opening is on the posterior part of the dorsum. The three 

 known species are parasitic on mammals one on the cat, one on the 

 rabbit, and the third on rats. 

 Notoedres muris Megnin. 



This is a rounded mite, with finely striate skin, a small triangular 

 rostrum; in front the four anterior legs project a little beyond the 

 body, and each ends in a long pedicellate sucker; the third and 

 fourth pairs of legs are not visible from above, and each ends in a 

 long bristle. There are a few short hairs around the anal aperture 

 and about ten others in front of these. The species measures about 

 0.3 to 0.4 millimeter long. 



It usually occurs about the ears and the genital organs of the host, 

 and has been taken from both the brown and black rat in Europe. 

 The Sarcoptes alepis Railliet and Lucet is the same species. 



DEMODECID^. 



Besides the mites above described, a form of Demodex has been 

 recorded from rats, but the species is not given. These mites are 

 very tiny, with elongate body, the posterior part annulate, the front 

 part with eight very short legs. They inhabit the hair follicles of 

 various mammals. That on the rat may have been only an accidental 

 occurrence of some species normally on another animal. 



