STROCTUUE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 369 
body. In some cases as many as ten of the Arachnids have 
been found on a single Hy, and if the movements of the 
insect are impeded by the presence of a number of the 
Chernes it will be easily understood that the life of the Hy 
will be curtailed thereby. Pseudo-scorpion idea have been 
observed feeding on the mites that infest certain species of 
Coleoptera, and it has been suggested that they associated 
with the flies for the same purpose, although I do not know 
of any recorded case of a fly infested with mites carrying 
Chernes also. If this were the case the Chernes would be 
a friend and not a foe of the Hy, as Hickson (1905) has 
pointed out. 
There are few records to support the view that the Chernes 
is parasitic on the fly. Donovan (1797) mentions the occur- 
rence of a pseudo-scorpionid on the body of a blow-fly, and 
Kirby and Spence (1826) refer to their being occasionally 
pai’asitic on flies, especially the blow-fly, under the wings of 
which they fix themselves. It is probable that the Chernes 
seldom reaches such a position of comparative security on the 
thorax of the fly ; should it succeed in doing so, however, it 
could become parasitic in the true sense of the word. As I 
have previously pointed out, little experimental evidence is at 
present available and further iiivestigation is necessary before 
it is possible to maintain more than a tentative opinion with 
regard to this association between the Chernes and the 
fly. It is obvious that the association will result in the dis- 
tribution of the Pseudo-scorpionid, but whether this is 
merely incidental and the real meaning lies in a parasitic or 
predaceous intention on the part of the Arachnid, as some of 
the observations appear to indicate, further experiments alone 
will show. 
2. Acarina or Mites borne by House-flies. 
As early as 1735 de Geer observed small reddish Acari in 
large numbers on the head and neck of M. domes tic a. 
They ran about actively when touched. The body of this 
mite was oval in shape, completely chitiuised, and polished; 
