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MB. A. D. MICHAEL ON THE LIFE-HISTOBIES 



Glycipliagi, 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 miuute 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 

 TyrogJyphus, 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 GlycipJiagi, 

 as opposed to the polished cuticle, setiform hairs, and usually 

 shorter tarsi of Tyroglyplii, and more especially by the females 

 of Glycipliagus possessing a central tubular projection from the 

 posterior margin which is absent from those of Tyroglyphus : 

 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 Tyroglyphus, as indeed Dr. Nalepa 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 ; 1 shall simply state 

 conclusions, referring to that paper for all proofs and other in- 

 formation on the subject. Hypopi 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 

 terudnated by hairs, not claws. Hypopi are most commonly found 

 adhering to insects, miriapods, &c., and they have been ultimately 

 shown to be a stage iu the life-history of some Acari of the genus 

 Tyroglyphus and one or two allied genera, although they are 



* " Tlie HT/pojms question," Journ. Linn. Soc, Zool. toI. xvii. (1884) pp. 



37i-ay4. 



