250 



THE PATHOGENIC FLAGELLATES 



forms the stomach and intestine of the invertebrate is substituted for 

 that of the vertebrate. Minchin holds that trypanosomes are never 

 found in the ahmentary tract of insects which do not draw blood, and 

 finds in this a further support for his hypothesis. 



All such speculations, while interesting and stimulating to further 

 research, are, however, unsubstantial, and generalizations cannot yet 

 be drawn with any safety. The following list of species, founded in 

 large part upon the species enumerated in Liihe's excellent paper on 

 these forms, shows what a large field for research this group presents, 

 and that "material" is at hand for investigators everywhere. 



The most plausible hypothesis concerning the origin of the trypano- 

 somes interprets them as more highly evolved organisms of the her- 

 petomonas or crithidia type. Like the latter they are characteristically 

 fluid-dwelling parasites either in the denser fluids of the digestive tract 

 of invertebrates (Trypcmoplasma borreli in the leech) or in the less 

 dense fluids of the blood. As crithidia and herpetomonas may lose 

 their motile organs and pass into a quiescent phase, or in the case of 

 H. donovani into a cell invading phase, so trypanosomes may assume 

 resting or encysted phases (e. g., T. grayi in the rectum of the tsetse) 

 or even the cell-invading phase (T. noctuse) in the blood. 



List op Species op Trypanosoma. 



