154 ARACHNIDS AND MYRIAPODS 



There are few records to support the view that the Ckernes is 

 parasitic on the fly. Donovan (1797) mentions the occurrence of 

 a Pseudo-scorpionid on the body of a blow-fly, and Kirby and 

 Spence (1826) refer to their being (jccasionally parasitic on flies, 

 especially the blow-fly, under the wings of which they flx them- 

 selves. It is probable that the Chernes seldnin reaches such a 

 position of comparative security on the thorax of the fly ; should 

 it succeed in doing so, however, it would become parasitic in the 

 true sense of the word. As I have previously pointed out, little 

 experimental evidence is at present available and further investi- 

 gation 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 distribution of the Pseudo-scorpionid, but whether this is 

 merely incidental and the real meaning lies in a parasitic or pre- 

 daceous intention on the part of the Arachnid, as some of the 

 observations appear to indicate, further experiments alone will 

 show\ 



Mites or Acarina borne f.y House-flies. 



Most careful observers and even casual observers have noticed 

 that house-flies are occasionally infested with small reddish mites 

 which are attached to theii- bodies in various positions. 



As early as 1735 de Geer observed small reddish Acari in large 

 numbers on the head and neck of M. domestica. They ran abt)ut 

 actively when touched. The body of this mite was oval in shape, 

 completely chitinised, and polished ; the dorsal side was convex 

 and the ventral side flat. Linnaeus (1758) called this mite Acai-tis 

 muscarum from de Geer's description, and Geoffroy (1764) found 

 what appears to be the same, or an allied species of mite, which 

 he called the "brown fly-mite." Murray (1877) describes a form, 

 Trombidium parasiticum, which is a minute blood-red mite para- 

 sitic on the house-fly. He says : " In this country they do not 

 seem so prevalent, but Mr Riley mentions that in North America, 



^ I have since endeavoured to throw some light on this question by keeping 

 Chernes and flies in small vials. In no case, however, did I observe the Chernes 

 feeding on the living fly, although they would feed occasionally on the dead flies. 



