2^56 



ARACHNOIDEA, 



CASE usually so infested by Gamasi, he found almost always Hypopi 



XiV 



on the parts of the body which the attacked insect had most 

 difficulty in reaching. He adds, ** but as is always the case, I 

 found more than I sought for, more especially larvae of Acari, of 

 which I had no idea, and whose ulterior form is precisely that of 

 the Acarids that hve in the perfect state on the same insects. 

 Thus, the Bombus lapidarius furnished Hypopi quite different 

 from those of Bombus terrestris." By beating the branches or 

 trees, on which certain Gamasi and Dermanyssi live, he found 

 other Hypopi ; and lastly, on at least one subterranean rodent, a 

 field-mouse (Arvicola subterranea), which has Gamasi as parasites, 

 he found corresponding Hypopi, but with the remarkable peculi- 

 arity, that, as the abdominal suckers would not answer in their 

 case to fix these mites, they were replaced by two salient striated 

 tubercules, as shown in the woodcut, which can approach each 



other like two lips, so as to lay hold 

 of a hair of the mouse, and so answer 

 the purpose fulfilled by the suckers 

 in the others. In conclusion, he 

 thinks, that he has shown that there 

 are Acari with eight feet, which are, 

 nevertheless, only the first age of 

 other well-known Acari, the Gamasi, 

 which differ from them as m.uch, at 

 least, as the Hydrachnidse differ from 

 their larvae. He describes eleven 

 species, which he divides into two 

 sections, one with the back divided 

 by a transverse line near the arti- 

 culation of the second pair of legs, in this respect resembling the 

 Tyroglyphi; the other not so divided. His Hypopus arvicola 

 has the transverse line across the back, but not the abdominal 

 suckers of either of the others, having, instead, the two tubercles 

 above described. 



llypopus arvicola. Copied from Dujardin. 



