THE HiEMOFLAGELLATES. 275 



have a body which is in complete agreement with that of Try- 

 panosoma. 



3. Lastly, what undoubtedly seems to be a transitional 

 stage in this disappearance of the anterior flagellum is seen 

 in Trypanoplasma cyprini (tig. 17h), where this organella 

 is short and delicate, and evidently undergoing reduction. 



While the evidence thus adduced points, in our opinion, 

 unmistakably to the derivation of at least some of the forms 

 included in the genus Trypanosoma from a Hetero- 

 mastigine ancestor, there is, it may at once be admitted, 

 one morphological feature which does^ at first sight, seem to 

 oppose this theory. The character in question is the varia- 

 tion in position of the kinetonacleus, especially during certain 

 developmental phases. 



In most species of Trypanosoma, the kiuetonucleus 

 occupies, in adult parasites, a position near the non-flagellate 

 end. Its position here, therefore, compares with that in the 

 simple Herpetomonadine forms (e. g. H. gracilis, jaculum, 

 and muscae-domesticge) and in Trypanoplasma in 

 exactly the same way as does that of the other cell-con- 

 stituents referred to above (where noticed) in the two sets of 

 cases. 



Were the approximately terminal position of this organella 

 constant, therefore, this character would be in complete 

 agreement with the other morphological ones, and would be, 

 undoubtedly, a very strong point in favour of the view 

 here taken. As it is, however, the kiuetonucleus varies 

 considerably with respect to its situation in the body. On 

 the one hand, in Herpetomonas subulata, some indivi- 

 duals of H. minuta and Trypanomorpha noctuse, 

 it has passed backwards almost as far as, or sometimes 

 even behind (posterior to), the trophonucleusj and, on 

 the other hand, in certain species of Trypanosoma 

 (e.g. T. inopinatum, T. rotatorium, T. transvaaliense) 

 it occupies a similar position on one side or other of the 

 trophonucleus, in more or less contiguity to the same. 

 Hence, having regard to these facts alone, it might reason- 



