THE GENUS TRYPANOSOMA 



245 



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

 provided with contractile myonemes. The non-flagellated end of the 

 cell may be pointed, as in T. thelleri, or rounded or blunt. The endo- 

 plasm frequently contains granules of chromatoid 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 number; 

 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 



Trypanosoma "Trypanozoon" theileri (Bruce), blood of cattle Tran^caiica<ia. X 3000. 

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



There are two different theories as to the phylogenetic history of 

 this well-marked and highly characteristic type of organism: one 

 deriving it from heteromonad forms like bodo or anisonema (Fig. 1 5 

 p. 43), the other from forms like herpetomonas and crithidia. According 

 to the first hypothesis, the trypanosome condition is brought about by 

 the union of the trailing runner, flagellum, or Schleppgeissel with the 

 cell body. If this were the case, then the flagellum end of the organism 

 would be posterior. A certain amount of evidence in favor of this point 

 of view is given by two interesting types of blood-dwelling parasites 

 of fishes, trypanoplasma and trypanophis, in both of which there are 

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

 attached to the body throughout its length and terminating as a 



