STRUCTURE, DEVELOPMENT, AND P-inNOMTCS OF HOUSE-FLAL 871 
apparently by their stomal regions. These specimens may be 
truly parasitic, as I am inclined to believe, since many Acari 
are parasitic in the immature state, although the adults may 
not be so; on the other hand this form of attachment may be 
employed as a means of maintaining’ a more secure hold of 
the transporting insect. 
8. Fungal Disease — Empusa muscae Cohn. 
Towards the end of the summer large numbers of Hies may 
be found attached in a rigid condition to the ceiling', walls or 
window-panes. They have an extremely life-like appearance, 
and it is not until one examines them closely or has touched 
them that their inanimate, so far as the life of the Hy is con- 
cerned, condition is discovered. These flies have been killed by 
the fungus Empusa muscae Cohn, and in the later stages of 
the disease its fungal nature is recognised by the fact that a 
white ring of fungal spores may be seen around the fly on the 
substratum to which it is attached. 'I'he abdomen of the fly 
is swollen considerably, and white masses of sporogenous 
fungal hypha) may be seen projecting for a short distance 
from the body of the fly, between the segments, giving the 
abdomen a transversely striped black and white appearance. 
The majority of flies which die in the late autumn — and it 
is then that most of the flies which have been present during 
the summer months perish — are killed by this fungus. Its 
occurrence, therefore, is of no little economic value, especially 
if it were possible to artificially cultivate it and destroy the 
flies in the early summer instead of being compelled to wait 
until the autumn for the natural course of events. 
Empusa muscae belongs to the grouj) Entomophthoreae, 
the members of which confine their attacks to insects, and in 
many cases, as in the case of the pi'esent species, are produc- 
tive of great mortality among the individuals of the species of 
cult to identify ininiature Ganiasids owing to the scarcity of knowledge 
as to their life-histories, hut he says that they are very like Dinycliella 
asperata Berk 
