OF GLYCIPHAGUS DO M ESTICUS AND G. SPINIPES. 



287 



very unlike all other sta<>es of Ti/roglijphi iu appearance. The 

 stage does not occur in the life-hiatory of every individual of a 

 species, but in a comparatively limited number of instances. 

 Megnin considered that the stage occurred when, from drought 

 or unfavourable circumstances, the colony w^as in danger of perish- 

 ing, and that the nymphs of Tyroglyphus had the power of turning 

 into Hypopi and so remaining until either the circumstances had 

 again become favourable in the place where they were, or until 

 they had emigrated into more suitable quarters — the Hypopus 

 being better able to endure drought &c., and more capable of 

 adhering to insects and thus escaping than the other stages of 

 the creature. I think that I proved by the investigations detailed 

 in the paper above referred to that this was an error, and that 

 unfavourable circumstances did not affect the question — the Hy- 

 popial stage being a provision of nature to ensure the distribution 

 of the species, occurring irrespective of adverse conditions, and 

 that it occupied the period between two ecdyses in the life-history, 

 commencing in the species which I was then studying at the 

 second nymphal ecdysis. 



Glyciphagus is not one of the genera in which a Hypopial stage 

 has ever hitherto been found to exist, except in tlie case of 

 G. Crameri described by me in 1886 * ; and this, as pointed out in 

 the paper in which I described it, is an extreme species of the 

 genus, which would hardly be included in the genus were it not 

 for the connecting-links, and wouhl undoubtedly fall within Hal- 

 ler's genus " Dermacarus " if that genus were retained. Of the 

 two species named in the title, one, G. spinipes, was first recorded 

 by Koch ; and, so far as we know at present, there is not any 

 difficulty in identifying it, and but little synonymy connected 

 with it. G. domesficus can, however, hardly be said to be in this 

 happy position : the synonymy of this species would probably be 

 voluminous ; but this is not the place to investigate it, beyond 

 what is necessary for identifying the species that I have been 

 experimenting upon. The species was originated by de Geer, 

 who called \t Acanis domesticus, the division of Tyroglyplius from 

 Glyciphagus not having been effected at that time ; one result of 

 this has been that numerous writers have identified the creature 

 with the common cheese-mite {Tyroglyplius siro, Linn.). Now, 

 however, that the distinction between the two genera is understood, 

 it is abundantly clear that de G-eer's species was a Glyciphagus ; 



* " Upon the Life-history of an Acarus, one stage whereof is known &sLabz- 

 dopkorus talpa, Kramer, &c.," Journ. R. Mic. Soc. 1886, pp. 377-390. 



