308 THE PROTOZOA 



same genus as T. cruzi, in which case the name Endotrypanum has 

 the priority over Schizotrypanum. In the present state of know- 

 ledge, data are lacking for deciding how far it is possible to employ 

 either multiplication by schizogony or an intracorpuscular habitat 

 as characters for defining genera of trypanosomes. An intra- 

 corpuscular habitat is probably commoner in trypanosomes than 

 has usually been supposed. It has been described quite recently 

 by Buchanan in T. brucii. 



Attempts to subdivide the genus Trypanosoma as a whole have 

 been based on the possibility that the trypaiiosome-type of structure 

 may have had two distinct phylogenetic origins, one through 

 Leptomonas and Crithidia from a cercomonad ancestor, the other 

 through Trypanoplasma from a heteromastigote or Bodonid type. 

 The trypanosome-form might be imagined to have arisen from 

 either of these two types. It could be derived from a form like 

 Trypanoplasma by loss of the free anterior flagellum, in which 

 case the flagellum of a trypanosome is to be regarded as posterior ; 

 on the other hand, if, in a form like Leptomonas, the kinetonucleus 

 and with it the origin of the flagellum, be shifted backwards to the 

 neighbourhood of the trophonucleus, and if at the same time the 

 flagellum runs forwards along the body connected to it by an un- 

 dulating membrane, a Crithidia-like form results, from which, by 

 still further displacement backwards of the kinetonucleus and 

 flagellum to near the posterior end of the body, a trypanosome- 

 form is produced in which the single flagellum is to be regarded as 

 anterior. It is therefore conceivable that the trypanosome-form 

 may comprise two morphological types, structurally indistinguish- 

 able, but entirely different in origin, and opposite in morphological 

 orientation of the body. 



From this point of view, Woodcock (395) subdivided trypano- 

 somes into two genera : Trypanomorpha, with cercomonad ancestry 

 and flagellum morphologically anterior ; and Trypanosoma, in a 

 restricted sense, with heteromastigote ancestry and flagellum 

 morphologically posterior. The genus Trypanomorpha included 

 only one species, T. noctuce of Athene noctua ; all other species of 

 trypanosomes were left in the genus Trypanosoma sens, strict. 

 Liihe put forward a classification based on similar conceptions with 

 different interpretations, and proposed three genera of trypano- 

 somes : Hcematomonas (Mitrophaiiow) for the trypanosomes of fresh- 

 water fishes believed to have a heteromastigote ancestry ; Trypano- 

 zoon for the trypanosomes of mammals, such as T. lewisi, T. brucii, 

 etc., regarded as having a cercomonad ancestry and an anterior 

 flagellum ; and Trypanosoma sens, strict, for the trypanosomes of 

 frogs and reptiles. T. noctuce,, on the other hand, he regarded, in 

 agreement with Schaudinn (see p. 390, infra], merely as a develop- 



