60 SANITARY ENTOMOLOGY 



among insects introduces an equally troublesome complication into the 

 study of the life histories of the heteroxenous nematodes parasitic in 

 higher animals, for which insects may serve as intermediate hosts. About 

 250 species of nematodes have been recorded as parasites of man and 

 domestic animals. Many of these require no intermediate hosts, but 

 some are heteroxenous parasites, and a number of these are known to have 

 intermediate stages in insects and closely related arthropods. In the 

 following discussion, in addition to the nematodes parasitic in man and 

 domestic animals, certain species parasitic in other animals are also con- 

 sidered because of the part played by insects in their life history. For 

 convenience they may be placed in two groups, (1) those in which the 

 eggs or first-stage larvae leave the body of the final host in the feces, and 

 (2) those in which the first-stage larvae occur in the blood or lymph of 

 the final host and leave the body through ingestion by bloodsucking 

 insects. 



1. Parasitic Nematodes Whose Eggs or Larva Leave the Body of the 



Filial Host in the Feces 



Protospirura muris (Gmelin, 1790) Seurat, 1915 



This nematode, parasitic in its adult stage in the stomach of various 

 species of rats and mice, is of special interest historically as being the 

 first parasite in whose transmission to its final host an insect was found 

 to be concerned. Stein in 1852 recorded the presence of encysted nema- 

 todes in the larvas of meal beetles (Tenebrio molitor). Leuckart (1867) 

 and Marchi (1867) fed eggs of Protospirura muris (Spiroptera obtusa) 

 to meal beetle larvae and followed the development of the young nematodes 

 up to the encysted stage found by Stein. This development is completed 

 in about six weeks after ingestion of the eggs. The development to the 

 adult stage was also followed in mice fed with the encysted nematodes from 

 meal worms. Johnston (1913) has recorded encysted nematode larvae 

 which appeared to him identical with those of P. muris in the body cavity 

 of a rat flea (Xenopsylla cheopis). 



Spirocerca sanguimolenta (Rudolphi, 1819) Railliet & Henry, 1911 



The adults of this nematode live in tumors of the stomach and 

 esophagus of the dog and the wolf. The eggs unhatched pass out of the 

 body of the dog in the feces. Grassi (1888) found encysted larval nem- 

 atodes in cockroaches (^Blatta ori^ntaiis) which he suspected were the 

 larvse of S. sanguinolenta. Dogs fed with these encysted nematodes after 

 five days showed the larvae free in the stomach ; after ten days the young 

 worms were further developed and were firmly attached to the mucosa 



