CHAPTER VII. 



THE PATHOGENIC FLAGELLATES— (Continued). 



THE GENERA HERPETOMONAS (INCLUDING "LEISHMANIA") 



AND CRITHIDIA. 



With these genera belonging to some of the more primitive forms 

 of the mastigophora, there is no question as to the animal nature, and 

 from the biological standpoint they form an extremely interesting 

 series of protozoa. Among them may be found all of the stages 

 leading from a free, flagellated, and celozoic mode of life to a non- 

 motile, intracellular, or cytozoic life, while some of them (H. donovani) 

 during the latter phase may give rise to fatal diseases in man. Again, 

 they are interesting in a zoological sense, in that here (crithidia) may be 

 found variations in cellular structure pointing toward that compli- 

 cated kinetic structure of the trypanosomes, the undulating mem- 

 brane. On the other hand, they show, through herpetomonas, a 

 close relation to free-living forms in stagnant water and belonging to 

 the family cercoraonadidse. Undulating membranes are uncommon 

 among flagellated protozoa, but are frequently found among ciliated 

 forms. Here, however, they represent quite different morphological 

 structures (Fig. 92). 



Novy, MacNeal, and Torrey ('07) hold that all forms of herpeto- 

 monas and crithidia are in reality trypanosomes, basing their conclu- 

 sion upon the fact that cultural forms of trypanosoma lack the undu- 

 lating membrane and appear in no wise different from these ordinary 

 flagellates of the insects' digestive tracts. Such a conclusion cannot be 

 allowed in any zoological sense, for at no time in the life history of any 

 species of herpetomonas or crithidia are stages present with char- 

 acteristic structures specific to the genus trypanosoma.^ 



The point of view held by Lfeger, Caullery and Mesnil, and some 

 others is quite different. According to this the trypanosomes are 



1 If species admittedly do not conform to a generic diagnosis, there is no possible reason 

 for enrolling them in such a genus where they obviously do not belong. What would a 

 zoologist say to a naturalist who claims that necturus and other perennibranchiate amphibia 

 are only species of amblystoma, on the ground that the larval form of the latter has gills? 

 And yet it is exactly this, in effect, that Novy, MacNeal, and Torrey claim for herpetomonas 

 and crithidia, and the high position which these investigators occupy in medical circles makes 

 an error like this particularly unfortunate. The group of trypanosomes is quite complicated 

 enough as it is, without the added diflSculties of other genera. 



