GENUS: TRYPANOSOMA 457 



the vertebrate being infected by accidentally ingesting the faeces of the 

 invertebrate or the invertebrate itself. In the former case the trypano- 

 somes are described by Duke (1913) as having an anterior station in the 

 invertebrate. Employing this suggestion, it will be convenient to describe 

 the others as having a posterior station. In the case of T. gamhiense in 

 Glossina palpalis, infection of the salivary glands follows an intestinal 

 phase of development (Fig. 216). In other trypanosomes {T. congolense), 

 also transmitted by species of Glossina, an intestinal phase of development 

 leads to infection of the proboscis alone, the salivary glands not being 

 infected (Fig. 217), while in others (T. vivax) there is no intestinal develop- 

 ment, the whole cycle taking place in the proboscis of the tsetse fly (Fig. 

 218). These three variations of development in the tsetse flies may be 

 used as a basis for classifying some of the pathogenic trypanosomes, as has 

 been done by Duke (1913) and Bruce (1914). Many of the trypanosomes 

 of cold-blooded vertebrates, as, for instance, T. inopinatum of frogs, are 

 transmitted by leeches. In these invertebrates the trypanosomes develop 

 in the stomach, and finally in the proboscis sheath (anterior station), 

 whence they gain access to the wound inflicted by the leech when it feeds 

 (Fig. 243). All these methods of infection by tsetse flies and leeches 

 may be spoken of as inoculative, since the trypanosomes are inoculated at 

 the time of biting. The other method of infection is contaminative, for 

 infection takes place through infected faeces or the invertebrate itself' 

 being ingested or, possibly in some cases, by faecal contamination of the 

 wound inflicted by the invertebrate. Thus T. lewisi develops in the flea, 

 leading to infection of the rectum (Fig. 199). Rats acquire the infection 

 by eating the faeces of the fleas. If the complete life-histories of all the 

 trypanosomes were known, it might be possible to group them according 

 to such data as have been just outlined. In the case of several trypano- 

 somes of small rodents, it is now known that the invertebrate hosts are 

 fleas, and that the infection of the vertebrate is contaminative as in T. 

 lewisi, while the trypanosomes of fish are carried by leeches, as in the case 

 of T. inopinatmn of the frog. In a certain number of cases, however, 

 the trypanosome is known only in its invertebrate host, but the existence 

 of a vertebrate host is rendered highly probable from the fact that these 

 flagellates are easily inoculable into vertebrates and produce a definite 

 infection comparable with the infections produced by inoculation of 

 trypanosomes from vertebrate to vertebrate. Thus, Lafont (1912) dis- 

 covered a flagellate in the gut of Conorhinus rubrofasciatus. When 

 inoculated to mice it produced a typical trypanosome infection, and 

 for this reason he gave it the name Trypanosoma hoylei. 



According to the scheme given on p. 346, the trypanosomes can be 

 grouped in the following manner: 



