Insects and Parasitic Diseases. 51>' 



that Johnston (1912, p. 76) has recorded a larval nematode resembl- 

 ing Habronema from Musca vetustissima. 



Mefliods of Infeciion of Flies. 



From the experiments herein detailed, it is obvious, in the case 

 of H. muscae and H. megastoma, since their intermediary host, M. 

 domestica, breeds chiefly in manure heaps that eggs containing 

 embryos or the very early larvae of these two helminths present in 

 the faeces' of the infected horse, are taken up during feeding b}^ 

 the larvae of the fly host, in which they continue their develop- 

 ment. 



In the case of H. microstoma and Stomoxys calcitrans this may 

 seem to be a more difficult matter to understand since Stomoxys 

 calcitrans, by reason of its piercing proboscis is apparently pre- 

 eminently fitted for the carriage of those parasites which pass some- 

 stage in the blood-stream of the host whence the adult fly derives its 

 food supply. We have no reason, hoAvever, to suppose either that 

 Habronema larvae ever occur in the blood-stream, or if they do, 

 that this would form their normal method of transmission. It is 

 evident on the other hand, that since Stomoxys does breed at times 

 in stable manure, the circumstances are propitious for the ingestion 

 of the embryo-containing eggs or young larvae of H. microstoma 

 from infected faeces by the larvae of Stomoxys calcitrans, as has 

 herein been shoAvn to occur, and that to a marked extent. 



It has been shown during these investigations that faeces infectecT 

 with the embryos of H. microstoma and H. megastoma remain-' 

 infective to the larvae of Stomoxys calcitrans and Musca 

 domestica respectively for periods up to fifteen days in each 

 species and in the case of H. muscae, the embryos have been shown- 

 to be infective to larvae of Musca domestica for periods up to eight 

 days, i.e., the largest period tested. It has been shoAvn further that 

 the larvae of both species of fly react to infection when from two" 

 days to nine days old. 



No evidence is foi'thcoming to show that the helminth larvae can 

 enter tlie fly-larvae by penetration or in any way other than by 

 ingestion. 



Beveloymenf within the Flies. 



Commencing from the earliest larval stage of each of the Hel- 

 minths under discussion, found in the larvae of the respective fly- 

 hosts, it has been found that the '' six stages " shown by Ransom,, 

 and confirmed by my own experiments to occur in the life of H- 



