28 Gerald F. Hill : 



made in the preceding pages, and although the methods employed 

 -are entirely different, there are no essential details in the results 

 upon which there is disagreement. 



Thus, the embryos passed out in the faeces from the horse are 

 taken up by the larvae of adults of Musca domestica, which have 

 oviposited on the faeces, which remain infective in this respect up 

 to at least eight days after leaving the rectum, the fly larvae being 

 known to react to infection when forty-eight hours up to nine days 

 old, and may l)e earlier and later. After a slight amount of 

 development in the faeces (Figs. 2 and 3), the end)ryo of Habro- 

 iievna muscae enteis the larva of Musca domestica (see Fig. 4). 

 Then it continues to develop in the fly pupa tliroiigh the various 

 stages shown in Figs. o-l^A, and in tlie adult fly as seen in Figs. 

 14-16, in wliich condition it is ready to develop in the stomach of 

 the horse, where such stages have Ijeen met with. 



Ransom (1913, p. 15) has suggested the possibility of infection of 

 the horse in three ways. Firstly, by ingestion of dead infected 

 flies, which he considers perhaps a common source of infection. 

 Secondly, by ingestion of the parasite in water or moist material. 

 Thirdly by ingestion of the parasite after its escape from the 

 fly whilst feeding upon the mucous niembrane of the horses' mouth. 



His experiments prove that possibly the second theory may 

 account for an occasional infection, but that such infection is not 

 •a normal occurrence. My own expei-iments do not support this 

 second theory at all, since as shown above, I have been unable to 

 obtain any .evidence of the escape of the parasite from the fly, 

 though Mr. Bull informs me that he has found such larval para- 

 sites to have escaped from flies kept in tubes, whether from living 

 or dead flies Avas not known. 



Concerning the third theoi-y. Ransom says that there is no evi- 

 dence, as yet, that larval Habronema escape from the fly whilst the 

 latter is feeding upon moist surfaces or matter. The evidence also 

 is still not forthcoming as the result of my experiments. 



From these and other observations made during the progress of 

 these investigations, the present writer lias no hesitation in express- 

 ing the opinion that the ingestion of both living and dead infected 

 flies provides the normal means by which the larval Habronema 

 iinds its way iuto tlie horse's stomach. 



That living flies and those which have recently succumbed are 

 quite commonly ingested by horses from the drinking tromzh and 

 manger is beyond question. On a frosty morning it is here a 

 common occun-ence to find numerous benumbed flies (both Musca 



