236 PARASITES OF FLIES 



manure heaps and hot-beds. No doubt these creatures are 

 distributed by flies, but it is at present uncertain whether they 

 feed on the fly, or merely cling to it by accident. Occasionally 

 more than one is found on a fly. 



(B) Internal parasites of ad^ilt flies, (i) Flagellates, 

 {a) Herpctonioiias. 



Species belonging to two genera, Herpetomonas and Crithidia, 

 of protozoon parasites have been found in the intestinal tracts of 

 non-biting flies. They have also been found frequently in the 

 intestinal tracts of biting flies. 



The genus Herpetomonas " contains a large number of flagel- 

 lates, which in their adult stages are characterized b)' the complete 

 absence of an undulating membrane, the single flagellum being 

 attached to the anterior end of the parasite by a short intra- 

 cellular portion. The blepharoplast is always anterior to the 

 nucleus usuall}' midway between it and the anterior end " 

 (Patton, 1909, p. 12). 



The t}'pe of this genus is H. viuscce-doinesticis Burnett. This 

 protozoon has been known as a parasite of the alimentary tract 

 of the house-fly for many years. It was first described by 

 Stein (1878), and later by Leger (1903) and Prowazek (1904), and 

 Patton (1908-9) has carefully studied its life history. It is 

 apparently comparatively rare in colder climates, but common in 

 the tropics. Patton states that "in the case of non-blood sucking 

 flies, which are foul feeders, it will be found that in certain 

 localities, for instance house-flies caught in the Indian bazaars, 

 100 °/o are infected with Herpetomonas innscce-doniestiece. The 

 ingestion of a large number of parasites results in increased 

 multiplication ; examinations of house-flies, in which almost the 

 whole alimentary tract is a living mass of young herpetomonads, 

 can leave no doubt on this point." 



" In order lo simplify the .study of these fiagellate.s of the genus Herpetomonas, 

 I have found it convenient to divide their life-cycles into three stages, preflagellate, 

 flagellate and post-flagellate. In the preflagellate stages they are round or oval bodies 

 with a large nucleus and round or rod-shaped blepharoplast ; they multiply by simple 

 longitudinal division... or by multiple segmentation. The flagellate stage is charac- 

 terized by the formation of a flagellum and multiplication of the resulting flagellates. 



