280 
MR. A. D. MICHAEL ON THE LIFE-HISTORIES 
Glyciphagi, the specific names of which are mentioned in the 
title of this paper ; it is the progress and results of those 
investigations which I now propose to record. 
The inquiry has involved a considerable amount of care and 
labour, not only from the inherent difficulties of isolating, rearing, 
and watching these minute creatures, but also because it has 
necessitated very numerous dissections of soft hyaline Acari, 
some of them less than the fifth of a millimetre in total length, 
and of the cast skins of these organisms. 
Glyciphagus is a genus of atracheate Acari , belonging to the 
family Tyroglyphidae, but which is distinguished from the genus 
Tyrogiyphus, or cheese-mites, by, inter alia , the rough cuticle, 
covered with granulations or vermiform markings, the pec- 
tinated or plumose hairs and long, slender tarsi of Glyciphagi, 
as opposed to the polished cuticle, setiform hairs, and usually 
shorter tarsi of Tyroglyphi , and more especially by the females 
of Glyciphagus possessing a central tubular projection from the 
posterior margin which is absent from those of Tyrogiyphus : 
some years ago I showed this to be a bursa copulatrix, a fact 
which, I believe, is now generally admitted ; the bursa doubtless 
exists in Tyrogiyphus , as indeed Dr. jNalepa has proved in one 
species, but it does not form an exterior projection. 
In order that this paper may be understood it is necessary to 
state, as shortly as possible, what a Hypopus is ; but as, in a 
former paper read before this Society*, I entered fully into the 
question, I do not propose to detail the various opinions held 
by different authors on the subject, nor the investigations which 
led me to the results given, except so far as is absolutely requisite 
in order that this paper may be intelligible ; I shall simply state 
conclusions, referring to that paper for all proofs and other in- 
formation on the subject. Iiypopi are minute Acari provided 
with a smooth, chitinous carapace, which conceals the whole, or 
almost the whole, of the creature ; they are somewhat arched on 
the back, but still considerably compressed dorso-ventrally ; the 
mouth-organs are rudimentary and the posterior pair of legs are 
terminated by hairs, not claws. Hypopi are most commonly found 
adhering to insects, miriapods, &e., and they have been ultimately 
shown to be a stage in the life-history of some Acari of the genus 
Tyrogiyphus and oue or two allied genera, although they are 
* “ The Hypopus question,” Journ. Linn. Soc., Zool. vol. xvii. (1884) pp. 
37 1-394. 
