OF GLYCIPHAGUS DOMESTICU8 AND G. SPINIPES. 
297 
under the most favourable couditious I could devise, and the 
Glyciphagi 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 
that 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 in 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 certaiuly 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. That 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 that 
the more adult nymph is formed within the Hypopus , and emerges 
