236 THE PATHOGENIC FLAGELLATES 



epithelial cells, to which they attach themselves often in large num- 

 bers (crithidia), or they may migrate into the cells, multiply there, 

 and cause serious trouble (Herpetomonas donovani). Because of 

 these dual motile and quiescent phases, they have quite upset the 

 taxonomic balance of many recent writers and have caused some of 

 the latter to sacrifice the well-known group, hemosporidia, while some 

 have gone, prematurely, to the length of entirely giving up the estab- 

 lished subphylum sporozoa as a group, although, indeed, even the 

 most conservative of systematists must admit that this group is not a 

 natural one. 



A. The Genus Herpetomonas.— The most primitive and the least 

 changed from the free-living forms of cercomonadine flagellates is the 

 genus which Kent, in 1881, named herpetomonas, characterizing it as 

 follows : 



"Animalcules free-swimming, elongate or vermicular, highly 

 flexible; the posterior extremity often the most attenuate, but not 

 constituting a distinct caudal appendage; flagellum single, terminal; 

 contractile vesicle conspicuous." To this he added the following 

 note: "This new genus is instituted for the reception of the form 

 figured by Stein, Tnfusionsthiere,' Abth. Ill, 1878, under the title of 

 Cercomonas muscco domestic^, and identified by that authority with 

 the Bodo muscce domesticoe of Burnett, and the Cercomonas mus- 

 carum of Leidy. The entire absence of a distinct caudal filament 

 serves, however, at once to distinguish it from the typical representa- 

 tives of either of the two last-named genera and approximates it the 

 more nearly to leptomonas or ophidomonas. A second minute form 

 recently discovered by Mr. T. R. Lewis in the blood of rats (Trypano- 

 soma lewisi) is provisionally referred to this generic group." Kent 

 Manual, p. 245. 



The contractile vacuole seems to have been more or less imaginative, 

 certainly subsequent observers have not described it and it is quite 

 possible that Kent and others mistook the vacuole about the blepharo- 

 plast for a contractile organ. Among the species that are now recog- 

 nized are the following : 



H. musccB domesticce, found in the intestine of the housefly. 



H. sarcophagoE, Prow. Intestine of meat flies. 



H. lesnei, L^ger. Malpighian tubules of Dasyphora pratorum. 



H. gracilis, Leger. Malpighian tubules of the sucking fly tanypus sp. 



H. campanulata, Leger. Intestine of larva of a sucking fly. 



H. jaculum, Leger. Intestine of the water bug Napa cinerea. 



H. donovani, Lav. and Mes. Intestine of cimex and cause of kala 

 azar. 



H. lygei, Patton. Intestine of the water bug lygaeus. 



Herpetomonas of culex sp., Patton. 



The most primitive and least changed from the free-living forms of 



