262 THE GROUSE IN HEALTH AND IN DISEASE 



heather and in the tarns and pools from which the Grouse drink, as before 

 mentioned. 



When faeces of infected chicks are voided, the ctecal or soft droppings are 

 heavily loaded with cysts, and not only do they foul the ground, heather, and water 

 in their vicinity, but, when dried, the powdery material produced may be dis- 

 seminated by the wind, and so oocysts and their contained sporocysts are dis- 

 tributed over comparatively large tracts of country. 



But other methods of producing richer local infections may be partly due to 

 insects. The agency of insects such as dung-flies has been observed in nature, and 

 also demonstrated experimentally. 



Scatophaga stercoraria, the dung-fly, commonly occurs on Grouse moors. The 

 eggs of the fly are laid in fasces, and hatch out there. The larvie are large and 

 somewhat active. They feed on the faeces of Grouse, which faeces may be infected 

 with coccidian cysts. Dissection of such larvae has shown the presence of oocysts 

 within their guts. When isolated larvae were first well washed and then allowed to 

 defaecate on a slide, the preparation of the faeces showed oocysts when examined 

 microscopically. Some of the pupas also contained coccidian spores in their guts. 

 The freshly hatched flies examined rarely showed spores, but as they proceed 

 almost at once to ingest faeces, they rapidly become agents for distributing the 

 spores. Dung-flies allowed to hatch out in the faeces of infected Grouse always 

 contained coccidian oocysts in their alimentary canal and faeces. 



Laboratory experiments were made with the blow-fly, Calliphora erythro- 

 cejihala. Eggs taken from the body of the parent fly were allowed to hatch out in 

 fiEces of an infected Grouse chick. The larvae greedily ingested the cysts, which 

 passed practically unaltered through their bodies. Some of the larvre which pupated 

 were washed very carefully and then dissected. They contained coccidian spores. 

 Adults were fed on the infected mateiial and oocysts were voided in their excrement. 

 The sjDreading of young flies, hatched infected, and of older ones that have fed on 

 infected material, may aid, then, in the dispersal of Coccidiosis. 



While experimental evidence of the action of Scatophar/a stercoraria and 

 Calliphora erythroccphala has been afforded in the laboratory, that is merely 

 confirmatory of what may occur on some moors. Here on Scots firs, heather, and 

 moss, numbers of flies are found, and dung-flies are known wherever Grouse 

 droppings ai-e to be found. The trail of birds can be tracked to some extent by the 

 coprophagous flies, while lines of infection are produced by the birds as they pass 

 down by small paths to their drinking places. 



