456 FAMILY: TRYPANOSOMIDiE 



G. morsitans, whereas the reverse is the case with T. brucei {T. rJiodesiense), 

 though in the blood of man the two trypanosomes resemble one another 

 closely. The power to infect invertebrates is not always as specific as 

 this, for T. lewisi can undergo its development, not only in the rat fleas, 

 but also in the dog and human fleas. This method of diagnosis has been 

 named by Brumpt (1914a) xenodiagnosis. He found during his investiga- 

 tions into the development of trypanosomes of fish, frogs, and snakes 

 that leeches often developed infections after feeding on animals in which 

 no trypanosome had been found. Similarly, with T. cruzi various species 

 of reduviid bugs may acquire infections when the trypanosomes are too 

 scanty to be found by microscopical examination in the animals on which 

 they fed. Bruce et al. (1913a, 1914^), in Nyasaland, employed the te.st 

 in a reverse manner by feeding batches of tsetse flies on susceptible animals 

 in order to determine the nature of the infection of the flies, the develop- 

 mental forms of the trypanosomes in the flies being more difficult to 

 identify than those in the blood of a vertebrate. 



CLASSIFICATION OF TRYPANOSOMES. 



At the present time our knowledge of the life-histories of the majority 

 of described trypanosomes is so imperfect that it is impossible to classify 

 them accurately in any system. Attempts have been made to divide the 

 group into separate genera. For instance, Llihe (1906) proposed to 

 separate the mammalian trypanosomes from all others under the generic 

 name of Trypanozoon. More recently, Chalmers (1918) has attempted a 

 still more elaborate classification, with the establishment of a number of 

 genera which are quite indeterminate. Such attempts fail to assist in the 

 clear understanding of this already complicated group, and only lead to 

 greater confusion. On morphological grounds alone all the trypanosomes 

 undoubtedly belong to one genus, Trypanosoma. Where anything like 

 a complete history is known, they are found to be polymorphic, exhibiting 

 in their development every type between the leishmania and the try- 

 panosome form. As a rule, reproduction by fission of any of these forms 

 may occur. Variations in the shape and size of the body, the relative 

 positions of the kinetoplast and nucleus, the degree of development of 

 the undulating membrane and flagellum, cannot be regarded as generic 

 characters. 



From the descriptions which will be given below it will be seen that 

 there are two main courses of development in the invertebrate. There is 

 the development which leads to infection of the biting parts of the inver- 

 tebrate, so that the vertebrate is inoculated during the biting act; and, 

 secondly, there is the development which leads to a hind-gut phase, 



