OF GLYCIPUAGUS DOMESTICUS AND SPfNIPES. 



297 



under the most favourable conditions I could devise, and the 

 Olyciphagi throve admirably ; but the cases containing Meg- 

 nin's cysts were formed rapidly and numerously in it ; from 

 which, and from the general experience acquired during the 

 somewhat lengthy observations above described, I feel assured 

 tbat with the Glyciphagi^ where the Hypopial stage is more or 

 less rudimentary, as with the Tyroglyphi, where it is an active 

 and functional one, the change to this stage is normal, although 

 not existing \\i the life-history of every individual, and is not 

 induced by desiccation or other unfavourable conditions ; but, on 

 the contrary, proceeds best and most rapidly when all conditions 

 are favourable. I do not deny that a creature may remain longer 

 in the Hypopial condition after it has been formed when the 

 surroundings are more suitable to that stage than to the ordi- 

 nary nymphal state, than it will when the converse is the case ; 

 I think this not improbable, although I have not seen any 

 evidence to prove that such is the fact. 



Conclusions. 



The results of the investigations detailed above may be sum- 

 marized as follows : — 



1. There is a Hypopial stage in the life-history of Glyciphagus 

 just as there is in that of Tyroglyphus. 



2. That this Hypopial stage is far less developed in Glyciphagus 

 than in Tyroglyphus, and is not, so far as is known at present, an 

 active stage. 



3. That we do not at present know whether it occurs in all 

 species, but it certaiidy does not occur in the life of every indi- 

 vidual of a species. 



4. That the stage is not the result of desiccation or other 

 unfavourable circumstances, but occurs as often under favourable 

 conditions. 



5. That the stage, in the species investigated, occupies the period 

 between the penultimate ecdysis and that immediately previous. 



6. Thar in G. spinipes the Hypopus is fully formed and capable 

 of moving its legs, but not of walking or other active movement ; 

 that it never becomes hard, or of the dark colour of the ordinary 

 chitin of active Hypopi. That, as a rule, it does not even leave 

 the skin of the young nymph in which it is formed ; but tliat 

 the more adult nymph is formed within the Hypopus, and emerges 



