:174 
C. (lORDlW TTKVVTTT. 
late autumn of one year and the summer of the next, is filled. 
A number of suggestions have been made, many of which 
cannot be accepted ; for example, Brefeld believes that the 
Empusa is continued over the winter in warmer regions, 
migrating northwards with the flies on the return of summer! 
In the case of En tomo phthora calliphora, Giard believes 
that the cycle is completed by the corpses of the blow-flies 
falling to the ground, when the spores might germinate in the 
spring a.nd give rise to conidia which infect the larvEe. Olive 
(1906) studied the species of Empusa which attacks a species 
of Sciara (Diptera) and found the larvae infected. He 
accordingly thinks that the disease may be carried over the 
winter by those individuals which breed during that period in 
stables and other favourable places. As I have shown, 
M. domestic a, under such favourable conditions as warmth 
and supply of suitable larval food, is able to breed during the 
Avinter months, although it is not a normal occurrence so far 
as I have been able to discover. If, then, these winter-pro- 
duced larvae could become infected they might assist in 
carrying over the fungus from one year to the next, and thus 
carry on the infection to the early summer broods of flies. 
This suggestion and the possible occurrence of a I’esting-spore 
stage appears to me to be the probable means by which the 
disease may be carried over from one “ fly-season ” to the next. 
E. muscfe, besides occuri'ing in M. domestica, has been 
found on several species of Syrphidm, upon which it usually 
occurs out-of-doors, as I have already mentioned. In addi- 
tion to these Thaxter records its occurrence in Lu cilia 
ctesar and Calliphora vomitoria. 
VI. True Parasites. 
1. Flagellata. Herpetomonas muscEe-domesticoe 
Burnett. 
This flagellate has been known as a parasite of the ali- 
mentary tract of M. domestica for many years. Stein 
(1878) figures a flagellate which he calls Cercomonas 
muscae-domestica, and identifies it with the Bodo muscae- 
