THE GENERA HERPETOMONAS AND CRITHIDIA 237 



flagellated intestinal parasites is the genus which Kent named herpeto- 

 monas. It is a widely distributed parasite of flies ; that of the common 

 housefly, Herpetomonas muscce domestic^, Burnett, is among the best 

 known of these species, largely through the observations of Prowa- 

 zek ('04). This organism is elongate and somewhat flattened at one 

 end, which gives rise to the single, long, vibratile flagellum (Fig- 93). 

 Apart from the nucleus and blepharoplast, the inner protoplasm has 

 no characteristic structures and the nucleus is of the characteristic 

 mastigophora type, with chromatin granules (often erroneously called 

 chromosomes) of more or less definite number. The blepharoplast 

 (fc) lies between the nucleus and the flagellum, and is frequently of 

 large size, while from it the base of the flagellum (rhizoblast) takes its 

 origin. Prowazek describes the flagellum as double, the two parts 

 being connected by a delicate membrane. If this were true, then, as 

 Minchin ('07) remarks, this organism would have to be enrolled in 

 some other genus than herpetomonas, but it is more than probable 

 that Prowazek described an early phase of division in which the 

 flagellum is precociously divided, as the typical form of the adult, 

 an interpretation supported by his own flgure (B) of a dividing form. 

 Patton ('08), furthermore, has been unable to confirm Prowazek's 

 observation, and finds that the flagellum is single both in H. muscce 

 domesticce and H. sarcophagw, but that it with the blepharoplast 

 divides first in reproduction. At the base of the flagellum, just outside 

 of the body, is a small basal granule (d), which in the cells with a 

 double flagellum was called the diplosome by Prowazek. 



Reproduction occurs by longitudinal division (Fig. 93, B). The 

 nucleus divides by a primitive process of mitosis, the granules being 

 equally distributed. This nuclear division is preceded by division 

 of the blepharoplast and of the flagellum, which in this case appears 

 to divide throughout its entire length instead of one being formed, as 

 in some trypanosomes, by outgrowth from the blepharoplast. 



Conjugation has been described by Prowazek as taking place 

 between forms which are not sexually differentiated beyond the fact 

 that one appears to be denser and larger than the other. During 

 conjugation the flagella are withdrawn and the nuclei undergo so- 

 called reducing divisions, similar in character to those occurring in 

 Trypanosoma noctuas (see p. 255). After conjugation a permanent 

 resting cyst is formed by the fertilized cell, and in this condition the 

 parasite passes from the intestine with the feces of the host. 



According to Prowazek, infection of new hosts takes place usually 

 by ingestion of these permanent cysts with the food ; but he also finds 

 that 5 per cent, of the flies examined and known to contain the allied 

 form H. sarcophagi had parasites in the body cavity and in the 

 ovaries as well as in the intestine. It is probable, therefore, that the 

 organism may be transmitted by inheritance. In H. lygci, on the 



