OF GLTCIPHAGUS DOMESTICUS AXD G. SPIXIPES. 
2S9 
considerably longer than those of G. spinipes. Thirdly, G. 
spinipes has an obtusely conical shape anteriorly, and is suddenly 
contracted between the second and third pair of legs ; G. domes- 
iicus has this form indicated but very slightly, being nearly as 
wide posteriorly as in the middle of the body ; the difference can 
only be well seen in living specimens. Fourthly, the bursa 
copulatrix of the female projects considerably more in G. domes- 
ticus (fig. 7) than in G. spinipes (fig. 15). Fifthly, G. domesticus 
is a trifle the larger, but this cannot be relied upon. Sixthly, 
the hairs of G. spinipes are more deeply serrated and stronger 
than those of G. domesticus. Seventhly, the tibiae of the first and 
second pairs of legs in G. spinipes each bear two large and thick 
curved, strongly-serrated hairs ; these are much less developed in 
G. domesticus. Eighthly, the second joints of the third pair of 
legs in G. spinipes each bear on the outside a peculiar hair or 
scale (fig. 14), shaped like a husk of corn, and placed with the 
concavity inward ; its outer surface is thickly clothed with fine 
hairs or processes : this structure is most developed in the female ; 
it has not, I thiuk, been mentioned by previous writers ; 
it is not found in G. domesticus. Ninthly, G. spinipes when 
placed on its back, or otherwise disturbed, has a rapid struggling 
or fighting motion with its first and second pairs of legs, a little 
of which is seen in its ordinary walk ; this style of movement is 
very characteristic of the species. 
The Tyroglyphidae, like most of the other Acari, have an inert 
period previous to each ecdysis ; during this time the creature is 
motionless and apparently dead, except that it does not shrivel 
up ; it is needless to say that a proper examination will disclose 
that the development of the creature in its next stage is pro- 
gressing inside the dead cuticle. 
GIltciphagus domesticus. 
During the month of May, 1885,, when I was examining some 
material which had been sent to me and which was swarming 
with G. domesticus in various stages, I observed that there were 
some which could only he classed as inert nymphs, but which had 
not quite the ordinary appearance of the creature in that stage ; 
the cuticle was more opaque, and seemed thicker and whiter, the 
back was more arched, the empty skin of the legs was more 
apt to be rubbed off, as if the inert stage had lasted longer than 
usual, giving a case-like appearance ; and I propose in this paper 
