296 



MR. A. D. MICHAEL ON THE LIFE-HISTOBTES 



complete, involving a return of all the organs to an egg-like state, 

 or whether it is only partial : the former has long been Megnin's 

 view, and he cites Claparede as confirming it ; but on reference 

 to the Swiss autlior's writings this does not seem to be by any 

 means certain. Dr. Nalepa, who has lately investigated the subject 

 with regard to the Tyroglyphidse, is strongly of opinion that it is 

 only partial*. I was formerly inclined to think, chiefly on 

 IMegnin's authority, that it w^as complete ; but more lately, having 

 paid some personal attention to the subject, I have come to a 

 conclusion wdth regard to the Oribatidse t more in accordance with 

 Dr. Nalepa's views. It is clear that Megnin has been observing 

 a process either identical with or very similar to what I have seen 

 in G. domesticus, but that not having found the more fully de- 

 veloped Hypopiis in G. spinipes he has naturally not recognized 

 that what he found was really a rudimentary Hypopus — the dif- 

 ference of the spherical form of the inert mass found by him in 

 his cysts from the more Hyp op) us -like form of the corresponding 

 mass found by me in G. do7nesticus may possiblj^ be accounted 

 for by his specimens having been examined more shortly after 

 the change commenced than mine were, or by his observations 

 having been made on G. cm^sor^ and that species not being really 

 identical with G. domesticus, although much resembling it, but 

 having the Hypopial stage even more rudimentary. 



It is quite possible that Megnin's idea that the inert nymph 

 when containing the Hypopial form, or, as he calls it, the cyst, 

 would be blown about by the wind may be correct : I do not see 

 that it would be more liable to be so blown about during this 

 than during any other ecdysis, except in so far as this may last 

 longer; but undoubtedly the creature within, protected by its 

 Hypopial skin, would bear more exposure and rough treatment 

 than the Acari would during other ecdyses. It will probably, 

 however, be gathered from the foregoing pages that I cannot 

 agree with Megnin that the change to the Hypopial, or as he 

 calls it encysted, condition is produced by desiccation or unfavour- 

 able surroundings. I have not conducted a series of experiments 

 expressly designed to determine this exact point, as 1 did with 

 the Tyroyhjphi ; but my material was not kept in any desiccated 

 or unfavourable condition ; on the contrary it was naturally kept 



* "Die u^natoniie der Tyroglyphen," Sitzun^^sb. k. Akad. Wien, i. Abth. 

 Juli-Heft, 1885, p. 151. 



t "British Oribatida'," Rav Society, vol. ii. (London, 1888), p. 604. 



