OF GLi’CIPHAGUS DOMESTICUS AND 6 . SPINIPES. 
287 
very unlike all other stages of Tyroglyphi in appearance. The 
stage does not occur in the life-history 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 was 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 the case of 
G. Crcimeri 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 would 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. domesticus 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 Greer, 
who called it Acarus domesticus , the division of Tyroglyphus 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 ( Tyroglyphus siro, Linn.). Now, 
however, that the distinction between the two genera is understood, 
it is abundantly clear that de Greer’s species was a Glyciphagus ; 
* “ Upon the Life-history of an Acarus, one stage whereof is known as Labi- 
dophorus talpce, Kramer, &c.,” Journ. R. Mic. Soc. 18S6, pp. 377-390. 
