THE GENUS TRYPANOSOMA 



245 



brane, which, as in Spirochria balbianii, is frequently, if not always, 

 providetl with contractile myonemes. The non-fiaoellated end of the 

 cell may be pointed, as in T. theiler'i, or rountled or blunt. The endo- 

 plasm frequently contains granules of chroniatoid material, and may 

 have a vacuolated appearance; little importance, however, has been 

 attached to these structural details of the endoplasm. The nucleus of 

 the cell, the element, that is, which superintends the vegetative pro- 

 cesses and sometimes called the " trophonucleus," is a clearly defined 

 morphological nucleus in which a nuclear membrane may be made 

 out in some cases, again not. The chromatin is usually in the form 

 of granules (miscalled chromosomes) of usually a definite numl)er; 

 but there is reason to believe that under satisfactory cytological 

 methods the chromatin is finely granular, surrounding a central 

 division centre, as in the majority of free flagellates (see p. 30). 

 Reproduction of the cell is by longitudinal division preceded by divi- 

 sion of the blepharoplast, kinetonucleus, and vegetative nucleus. 



Fig. 97 



Trypani>.<()iua ■■Tryi)anuz<)un" theileri (Bruce), blood of cattle Transcaucasia. X 3000. 

 (After Liihe.) k, kinetonucleus; (, trophonucleus; u, undulating membrane. 



There are two dill'crent theories as to the phylogenctic history of 

 this well-nuirked and liighly characteristic type of organism: one 

 deriving it from heteromonad forms like bodo or anisonema (Fig. 15 

 [). 4.3), theother from formslikeherpetomonasandcrithidia. According 

 to the first hypothesis, the trypanosonu* condition is brought about by 

 the Miiion of the trailing ruinier, flagclliiin, or Sclilrppr/rissrI with the 

 cell body. If this wi-re the case, then the fiagelliini end of the organism 

 would be posterior. A certain amount of evidence in favor of this |)oint 

 of view is given by (wo interesting types of blood-dwelling parasites 

 of fishes, trypanoj)lasma and trypanophis, in i)o(li of which there are 

 two flagella, one directed in advance at the anterior end, the other 

 attaelied to the bodv (lirouii'lioiit its jeniflh and terniiiiatini;' as a 



