HERPETOMONAS MUSCARUM 



367 



has completed the first division. In this manner, organisms with four 

 flagella and a single dividing nucleus may appear, and give the impression 

 of a dividing biflagellate organism. A similar condition is sometimes 

 seen in trypanosomes dividing actively in the blood of inoculated rats, 

 where large forms may occur with four nuclei, four kinetoplasts, and four 

 membranes and flagella. That the explanation given of the biflagellate 

 appearance is the correct one is borne out by the fact that in flies, where 

 active multiplication is not in progress, the flagellate has only a single 

 flagellum. 



It is in the leptomonas form that the flagellate is most commonly seen 

 in flies. As pointed out by the writer (1913a), the kinetoplast may change 



Fig. 170. — Herpetomonas muscarum of House Fly (x ca. 2,000) : Transformation 

 OF Leptomonas into Trypanosome Forms, (After Wenyon, 1913.) 



its anterior position for one near the nucleus, in which case the axoneme 

 passes along the surface of the body (Fig. 170). Such forms have the 

 crithidia structure, though an undulating membrane, as a definite band 

 of cytoplasm, is not actually present. With further migration backwards 

 of the kinetoplast, trypanosome forms are produced. The conditions 

 under which this takes place are not known. The occurrence of these 

 three phases has been noted in many allied flagellates. Some observers 

 believe they represent distinct species, but the bulk of evidence is in 

 favour of regarding all the forms as belonging to the cycle of the one 

 flagellate. Fig. 170 shows the various transition forms in an infection 

 where the leptomonas and the trypanosome types both occur (see also 

 Fig. 155). Rosenbusch (1909) noted these different forms in the flagellate 

 of the house fly, which, on this account, he termed Crithidia musccB 

 domesticoe. Becker (1923c) has confirmed these observations, while the 



