44 Gerald F. Hill : 



iiU on the result, as the Morm larvae were actively alive. Stomoxys 



«calcitrans exclusively was used in one experinxent, with the result 

 that 100% of the individuals subsequently examined were found to 

 be more or less heavily infected. In another experiment both 



.species of fly larvae weie introduced at the same time to a culture 

 of H. microstoma, with the result that 100% of the Stomoxys were 



-heavily infected, whilst the Musca doniestica Avere negative. In all, 

 71 Stomoxys larvae, pupae and adult flies were examined, of which 

 number 48 were infected. 



In the other two experiments (Nos. 15 and 16), a double culture. 



I.e., of Habronema muscae and of Habicnema microstoma, was given 

 as food to Musca doniestica and Stomoxys calcitrans, in the same 

 cage. Both of these experiments show undoubtedly that while 

 Habronema muscae only occurs in Musca doniestica, even when 

 Stomoxys calcitrans is in the presence of an intense infection, 

 Habronema microstoma occurs almost entirely in Stomoxys cal- 



<'itrans, but also rarely in Musca doniestica. 



Upon the results of these experiments, suppoited by the finding 



of what was almost certainly a larval H. microstoma in a naturally 

 infected Stomoxys fly (c.f. page 32), and further supported by the 



results of the experiments recorded on pages 16. 17, 18, 31 and 32 

 of this Report, the writer bases his conclusion that Stomoxys cal- 

 citrans is the principal intermediary host of H. microstoma, and 

 that Musca doniestica only occasionally (possibly only accidentally) 

 acts as an intei'mediary. 



In arriving at the first conclusion the writer has not lost sight of 

 the fact that deposits of fi'esh horse faeces are not the usual l)reed- 

 ing place of Stomoxys calcitrans. It is well known tliat this fly 

 breeds frequently, if not generally, in decaying grass, straw, and 

 similar matter, and also in loose soil contaminated by stable 



•drainage. The larvae and pupae are to be found commonly, how^- 

 ever, in the older portions of manure heaps, and in such situations 

 as ai-e to be found in croAvded horse yards. It has been proved 



'during these investigations, that under certain conditions, 



-embryonic H. microstoma remain infective in faeces for a period 



■of at least fifteen days. 



The fact that fresh faeces are not usually used as a breedinc: 



•ground by Stomoxys calcitrans offers no obstacle to Stomoxys cal- 

 citrans acting as a natural intermediary host of H. microstoma; 

 rather, this with other facts mentioned above, suggests the only 

 feasible explanation of some phenomena in the life of this form 

 which do not appear to be othei'wise explainable, namely, the 



