74 THE HOUSE FLY DISEASE CARRIER 



"Twenty-six dipterous larvae (species not deter- 

 mined) from horse manure which were examined for 

 the presence of nematodes were all free from infection 

 with H. muse a. Thirteen larvae of Musca dorncstica 

 and several pupae were examined with negative results. 

 These were bred from house flies confined in a dish 

 with horse manure which had previously been boiled 

 to destroy any fly larvae or nematodes which might 

 have been present. That some of the flies were infested 

 with Habronema was determined by examining a num- 

 ber after oviposition had occurred. An undersized 

 male which developed in the culture just referred to, 

 the only adult that was obtained in this culture, was 

 examined with negative results. 



"That infection with Habronema musce is acquired 

 during some stage prior to the imago was proved by 

 the discovery of the parasites in a fly caught just as it 

 was emerging from the pupa (No. 9, referred to 

 above). Beyond this fact the observations made by 

 me (made incidentally in the course of another in- 

 vestigation) have proved little as to the life history of 

 the parasite. On several occasions I have placed the 

 worms taken from flies in water and in horse manure, 

 but in no case was it observed that any further develop- 

 ment occurred. The worms invariably died within a 

 few days. It would seem, however, that the larval 

 stage of the parasite which is found in the fly must in 

 some way escape from its host, reach sexual maturity 

 either as a free living form or in another host, and 

 produce young which find their way into other flies 



