234 



ARACHNOIDEA. 



CASE on the underside, make them all take the same position, slightly 

 inclined, with their anterior feet in the air. If they are touched, 

 they set a-running ; but in place of finding these mites on the 

 house-fly, as De Geer had done, it was exclusively on the stable- 

 fly, Musca stabulans, that Dujardin found them in Paris, in 1846 

 or 1847, in a neighbourhood where there were many stables. 

 That fly appeared infested by the Hypopus in such numbers^ that 

 out of three, it was rare that two or more were not found charged 

 with them, while the house-fly, and several other species of flies, 

 and of Anthomyia, which were quite as abundant, never furnished 

 him with a single individual. In the species on that fly the four 



anterior feet are disproportion- 

 ately robust, and terminated by 

 a single strong claw ; the legs of 

 the third pair are 

 couched in a for- 

 ward direction, 

 under the margin 

 of the body, which 

 conceals them en- 

 tirely, and those of 

 the last pair termi- 

 nate in a long hair, 

 instead of a claw ; 

 but in other species 

 all eight legs have 

 a claw. The haunclies are contiguous, and usually form a thick 

 median line, but the most extraordinary part of the whole is the 

 head, which is produced into a flat and narrow blade, cut square at 

 the extremity, and from the angles of which proceed two diverging 

 bristles or hairs, but without any trace of mouth or even rudimentary 

 oral organs. Still, although no trace of opening can be seen in this 

 blade, it occupies the place and has a good deal of the appearance 

 of a sucking apparatus. Near the posterior margin of the under 



Hypopiis mnscarum. 

 Copied from Dujard.n's figure. 



Lip of Hypopus. 

 Conied from 



figure by Dujardin. 



