148 BRITISH TYROGLYPHID.E. 



which however he subsequently suppressed, finding it 

 to be only a Hypopus. 



Gervais * next described a supposed new species of 

 Hypopus, which genus oddly enough he associated with 

 Tyroglyphus, although without having any idea of the 

 real connection subsequently ascertained to exist be- 

 tween them ; it must be admitted that he also joined 

 certain other genera to Tyroglyphus which were not in 

 any way related to it. 



So far, except for the remark of Duges above 

 quoted, every one had treated Hypopus as a mature 

 Acarus. 



Dujardin returned to the subject in 1847 or before, 

 but his next paper was not published until 1849.1 

 This memoir was far the most careful study of 

 Hypopus made up to that time, and probably no better 

 drawings of Hypopi have ever been published. 

 Dujardin recognised that at the posterior end of the 

 ventral surface each Hypopus of the ordinary class 

 was provided with a plate of thicker chitin than the 

 remainder of the ventral surface, and that this plate 

 was situated between the anus and the hind margin ; 

 he also observed that the plate was pierced to allow the 

 passage of suckers, which were mostly within the area 

 of the plate but sometimes a few just outside it, and 

 that these suckers varied greatly in number, arrange- 

 ment, size, and other details; so that one Hypopus 

 might be distinguished from another by them ; and 

 that in the case of creatures similar to Koch's Homopus 

 the suckers and sucker-plates were replaced by two 

 clasping plates ; he saw that the Hypopi readily and 

 rapidly attached themselves to polished surfaces by 

 their ventral suckers, and held so tenaciously that 

 they were difficult to detach. Dujardin found great 



* In "Histoire naturelle des Insectes apteres," Walckenaer, t. 3 

 (1844), p. 265, in ' Suites a Buffon.' 



f " Memoire sur des Acariens sans bouche dont on a fait le genre 

 Hypopus, et qui sont le premier age des Gamases," in ' Ann. Sci. Nat.' 

 (1849), 3e ser., t. xii, pp. 243 250. " Additions au Memoire sur les 

 Hypopes," ibid., pp. 259266, pi. ii. 



