Insects and Parasitic Diseases. 43^> 



This is apparently the final larval stage of H. uiicrostonia in the- 

 body of the fly, and the stage comparable Avith Kansom's 6th stage 

 of H. muscae. Although larger larvae are found in flies, no fur- 

 ther developmental changes, other than a general increase in size, 

 have been observed in them. It is presumed, therefore, that in this 

 stage the parasite is ingested by tlie. horse, and tliereafter continues 

 its development in the stomach of the definitive host. 



Fig. 33 illustrates the posterior end of a parasite found on the- 

 same day and in the same culture as the larvae shown in Fig. 

 32. Although the former Avas somewhat larger (see Table 2, Speci- 

 men 5), both Avere evidently in the same stage of development. 



The maximum length knoAvn to tlie Avriter to be attained by the- 

 larval AA-orm Avithin the fly is 1.H15 mm. (see Table 2, Specimen 1). 

 A larvae of this length Avas found on January 16th in a fly Avhich 

 emerged tAAo days previously from the same culture as the tAvo last 

 mentioned parasites, i.e., Experiment No. 12. Other larvae from 

 the same fly measured from 1.584 mm. to 1.600. 



The final larval stage of H. microstoma in the body of the- 

 Stomoxys fly measures from 1.570 mm. to 1.815 mm. long, and" 

 although considerably shorter than the final larval stage of H. 

 muscae in the body of Musca domestica, it is in the same state of 

 advancement as the latter, as shoAvn, e.g., by the presence of the 

 characteristic spinous-tipped tail. 



Excepting only the earliest stage in tlie body of the fly-larvae 

 (c.f. Fig. 20), all the larval stages of H. microstoma knoAvn to- 

 the Avriter occur sometimes in CA'sts. 



Summary and Discussion. 



From an analysis of the experiments carried out to determine- 

 the relationship) of Musca domestica and Stomoxys calcitrans to 

 the embryos of H. microstoma, it Avill be seen that Musca domestica 

 exclusively AA'as used in five experiments. In tAV'o cases no infection 

 took place, Avhile in the remaining three cases a total of only three- 

 individuals became infected, each Avith a single parasite. In all,. 

 419 Musca domestica larvae, pupae, and flies Avere examined, Avith 

 the result stated. In one of these experiments Musca domestica 

 larvae failed to become infected in a culture, Avhich subsequently 

 infected 100% of tlie Stomoxys calcitrans examined; certainly the- 

 tAvo species of fly larvae AA'ere at different ages, but other experi- 

 ments Avith larvae of the same age of the tAvo species together, Avould 

 lead one to believe that the age of the fly larvae had noi influence at 



