RELATION OF INSECTS TO THE PARASITIC WORMS 65 



come infested by eating the eggs of the parasite which are passed in the 

 feces of infested pigs, donkeys, and dromedaries. As in the case of 

 Spirocerca sangumolmta Seurat finds encysted larvse of P. sexalatus in 

 various vertebrates in Algeria, particularly reptiles and insectivores. 

 Their presence in these animals he would explain in the same way as he 

 explains the presence of the encysted larvae of S. sangumolmta in such 

 animals, that is, the larvas present in insects devoured by the animals in 

 question are unable to continue their development as they would in pigs 

 and other suitable hosts. On the other hand they do not succumb in their 

 strange environment nor do they pass through the alimentary tract with 

 the feces but penetrate into the walls of the stomach and into other tissues 

 and become reencysted, surviving in this condition more or less indefinitely. 

 They may thus be considered parasites that have gone astray but still 

 capable of existence in their abnormal environment. The possibility of 

 their developing to maturity after reencystment in a strange host if this 

 animal should be eaten by a pig has not been substantiated experimentally. 

 Seurat (1916) has counted 4,880 larvje identified as P. sexalatus in a 

 single beetle, Scarabceus (Ateuchus) sacer. In addition there were 68 

 larvse of Spirocerca sanguinolenta in the same beetle, making a total of 

 4,948 larvae in the one insect. 



Hahronema musccE (Carter, 1861) Diesing, 1861 



This nematode in the adult stage occurs in the stomach of horses and 

 other equines, commonly in association with another closely related 

 species, H. microstoma. The life history of H. muscce has been shown to 

 be as follows (Ransom, 1911, 1913; Hill, 1918; Bull, 1919): The eggs 

 or the larvae pass out of the body of the host in the feces. They enter 

 the bodies of the larvse of the common house fly, probably being swallowed,, 

 though the mode of entrance has not been determined by direct observa- 

 tion. The worm larvse grow and develop in the developing flies and at 

 about the time the adult insects emerge from the pupal stage the larvae 

 reach the infective stage. In this stage they are most commonly found 

 in the proboscis. The ingestion by horses of flies harboring the larvaj 

 brings the young parasites into the location where the adult occurs, 

 and presumably this is the common method by which the larvse reach their 

 final host. The frequent swallowing of flies by horses is an undoubted 

 fact. The mouths of horses are very attractive to house flies especially 

 while the horses are eating, as any one can determine by a few minutes' 

 observation of the animals during the fly season. There is also another 

 possible and very probable way in which the larvas are transferred to 

 horses, suggested of course by the habit of the larvs of congregating 

 in the proboscis of the fly. We may expect that it will be demonstrated 



