THE GENUS DEMODEX. ]7 



D. canis, I), hnr/ior, D. cati, I), phylloides, I), bonis, and I), equi. In 

 J), muscidi the male orifice is usually situated a little further back, 

 being above the second pair of legs, whilst in D. muscardini and 

 D. cuniculi it is still furtlier back on the dorsal surface, being placed 

 above or slightly in front of the interval between the second and tliird 

 pairs of legs. The male aperture is sometimes guarded by an operculum 

 or fliip, usually conical or semicircular in shape. lu D. bovis, and 

 probably also in other species, the operculum consists of a median trian- 

 gular lobe and two small lateral lobes (in front), the penis pushing itself 

 between these lobes when protruded, the lateral lobes serving to keep the 

 penis in the right direction. Two pairs of minute but distinct swellings 

 or tubercles are present on the dorsal surface of the cephalothorax of the 

 male, whereas they are absent in the female ; they seem too small to serve 

 as suckers or clasping organs. These structures aie figured by Megnin 

 (see his 'Les Parasites', figs. 1 & 4, pi. xxvi.). Very similar circular 

 appearances are to be seen in Psorergates and Mijobia, near the male 

 sexual orifice — possibly they are the openings of glands. 



The female sexual orifice is a distinct longitudinal slit situated at 

 the anterior end of the ventral surface of the abdomen just behind the 

 coxcC (epimera) of the last pair of legs. It is sometimes bordered by 

 sliglitly elevated areas, and may be defined anteriorly by a slight 

 curved line. 



TAXONOMY. 



The different forms of Dcmodex have been considered to be varieties 

 of a single species by several authors who have studied tlie genus, but 

 in reality most of them seem to be quite distinct species ; some of 

 the forms regarded as varieties in this work may, however, have to be 

 merged as synonyms. A useful character is afforded by the pair of 

 dorsal spines on the capitulum (or rather on the palp), for they differ 

 in length and shape in some of the species (text-fig. 4, p. 14). The 

 proportions of the body should also be taken into account, especially 

 those of the capitulum and cephalothorax, although the former 

 varies somewhat in the same species, its shape being slightly 

 chan<'-ed when fully protruded or retracted. On the other hand, the 

 shape of the abdomen varies considerably, and can be easily altered by 

 the mite during life, and is also easily distorted when the specimen is 

 being mounted for the microscope. The shape of the epimera may 



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