296 
MR. A. D. MICHAEL ON THE LIFE-HISTORIES 
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 ; hut on reference 
to the Swiss author’s writings this does not seem to be by any 
means certain. Dr. Nalepa, who has lately investigated the subject 
with regard to the Tyroglyphidae, is strongly of opinion that it is 
only partial*. I was formerly inclined to think, chiefly on 
Megnin’s authority, that it ivas complete ; but more lately, having 
paid some personal attention to the subject, I have come to a 
conclusion with regard to the Oribatidae 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 Hypopus 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 Hypopus- like form of the corresponding 
mass found by me in G. domesticus may possibly 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. cursor, 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 I did with 
the Tyroqlyplii ; but my material was not kept in any desiccated 
or unfavourable condition ; on the contrary it was naturally kept 
* “Die Anatomie tier Tvroglyphen,” Sitzungsb. k. Akad. Wien, i. Abtb. 
Juli-Heft, 1885, p. 151. 
t “British Oribatida?,” Ray Society, vol. ii. (London, 1888), p. 604. 
