103 



The larvae of H . muscae and H. megastoma were found 

 to possess very similar appearances. H. megastoma was 

 usually slightly shorter than H. muscae, possessed a longer 

 pharynx and a shorter anterior oesophagus, and the nerve ring 

 was situated nearer the anterior end than in H. muscae. Both 

 species of larvae possessed longitudinal ridges in the cuticle. 



It is doubtful if these small differences in the appearances 

 of the two larvae would prove sufficient for the purpose of 

 differentiating larvae taken from granulomata, as in this case 

 the larvae usually show some retrogressive changes and exam- 

 ination is more difficult. 



Larvae of H . microstoma were found to be shorter than 

 the larvae of the other two species, and the absence of 

 longitudinal ridges in the cuticle offers a means for absolute 

 differentiation between this larvae and those of the other two 

 species. 



Escape of the larvae from the proboscis of flies was found 

 to depend upon rupture of some portion of the organ, probably 

 the thinner citinous membrane on the interior surface of the 

 labium. When this rupture was produced artificially the 

 larvae rapidly made their escape into any moisture at hand, 

 provided the temperature was sufficient to produce activity in 

 the larvae. The escape of larvae from the proboscis under 

 natural conditions was not demonstrated. 



The larvae when developed into the final stage migrated 

 to the head and proboscis. This may suggest that the larvae 

 abandon the intermediate host in somewhat the same manner 

 as Filaria larva do, but observations do not lend support to 

 this suggestion. The migration to and situation in the 

 proboscis of flies seems to be a common feature in the develop- 

 ment of Nematodes. For example, Patton and Cragg (1913) 

 have observed the development of the embryos of a species of 

 Oxyuris in Musca nebulo. The embryos are ingested by the fly 

 larvae, and the worms undergo their evolution in the pupae. 

 When the flies hatch out they are infested with adult parasites, 

 which cause paralysis of the proboscis on account of their 

 accumulation in this situation. 



The larvae apparently do not possess the power of 

 penetrating the structures in the proboscis of flies. Rupture 

 of the proboscis appears to depend upon the pressure exerted 

 by the larvae, which pressure would be in direct proportion 

 to the number of larvae present and their activity. Nor do 

 the larvae appear to be capable of penetrating other objects 

 such as filter paper. 



Larvae do not appear to live in saline solution, horse 

 serum, or water for longer than two or three days, and rarely 

 as long as seven days. The longevity of the larvae outside the 



