(128) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-PLY. 369 



body. In some cases as many as ten of the Arachnids have 

 been found on a single fly, and if the movements of the 

 insect are impeded by the presence of a number of the 

 Ch ernes it will be easily understood that the life of the fly 

 will be curtailed thereby. Pseudo-scorpionidea 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 fly, 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 

 parasitic 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 investigation 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. domestica. 

 They ran about actively when touched. The body of this 

 mite was oval in shape, completely chitinised, and polished ; 



