THE HiEMOFLAGELLATES. 281 



The course of evolution of the Heematozoa (as a whole) 

 in the blood of the Vertebrate appears to have been charac- 

 terised by the acquisition of an intra-cellular phase, together 

 with the capacity for multiplication while in that condition. 

 In such cases the subsequent tendency has evidently been to 

 develop the gregariniform or HEemosporidian phase at the 

 expense of the trypaniform or Hfemoflagellate one. For, on 

 carefully reviewing the evidence set forth in Section IX, it 

 seems scarcely open to doubt that there is a very close 

 phylogenetic relationship between the Haemoflagellates and 

 the Hgemosporidia, and that, moreover, in some cases there 

 is an actual ontogenetic connection between the two types of 

 form at the present day.^ 



host, or that it is not still obliged to return, if only at rare intervals, to 

 such a habitat, in order that, by sexual conjugation, the stock may be rein- 

 vigorated. The direct mode of transmission, most probably a secondary 

 acquirement, is readily accounted for by the peculiar superficial distribution 

 of the organisms (see above, p. 176). It must be borne in mind that this is 

 the only species which is known to be able to traverse healthy mucous 

 membranes, and this itself is against the derivation of Trypanosoma 

 fi'om an intestinal or entero-ccelomic. Vertebrate form. 



' Novy and McNeal (81), basing their view upon the results of their 

 cultural methods of work, conclude that there is no connection between 

 Cytozoa (Hsemosporidia) andTrypanosomes. They disbelieve in Schaudinn's 

 work, and think that this author was misled by working with " impure 

 cultures," as they regard the conditions in which the parasites occur in 

 their natural hosts. But, as Mesnil says, the presence of the characteristic 

 Hsemosporidian pigment in the trypaniform phase is a fact very difficult to 

 explain away. Again, Novy and McNeal consider that the appearance of 

 Flagellate forms in Eogers' culture of " P." donovani was merely a coin- 

 cidence, indicating the existence of a variety of human trypanosomosis 

 hitherto unknown, the two parasites being quite distinct ! The ample con- 

 firmation which both these important researches have already received 

 sufficiently disposes, we think, of the above view. 



It is, of course, very probable that there are Trypanosomes of birds (as 

 of other Vertebrates) which have no Hsemosporidian phase. It is not safe, 

 however, to argue that there is no connection between a given Hsemoflagel- 

 late and a given Haemosporidian from the negative evidence obtained by 

 cultures and their injection. For it is most unlikely that the further deve- 

 lopment of the parasites can go on in an artificial medium as successfully 

 and as normally as in the Insectan host, to which their biology is specially 

 VOL. 50, PART 2. NEW SERIES, 20 



