282 H. M. WOODCOCK. 



It is^ indeed; possible to construct what may be regarded 

 as stages in the direction of evolution thus outlined. The 

 first step is shown by those forms which possess resting, 

 attached phases (Try panoplasma almost certainly, and 

 probably some species, at any rate, of Trypanosoma, 

 e.g. T. equinum and T. equiperdum). A stage in 

 advance is exemplified by Trypanomorpha noctuae and 

 Trypanosoma ziemanni; these parasites become, for a 

 portion of their life, intracellular, but do not multiply 

 asexually in this condition. On the other hand, it appears 

 very probable from Billet's work (p. 251) that certain Amphi- 

 bian parasites possess (as Hsemogregarines) typical schizo- 

 gony, and this may be also the case in some Piscine forms. 

 Here the trypaniform phase is very likely much less in 

 evidence, and assumed (in the blood) only at rare intervals. 

 Probably about this level, too, come the Piroplasmata, 

 which are very interesting in that some of them retain the 

 nuclear dimorphism while iu the intracellular phase. Lastly, 

 a trypaniform phase in the life-cycle can only be recognised 

 with difficulty, in the sporozoites or merozoites (Plasmo- 

 dium vivax, possibly other malarial pai"asites and certain 

 Haemogregarines [cf. p. 253]); or, in other cases, may be 

 quite lost. 



It will be gathered from the above remarks that, with the 

 advance of our knowledge, it may well become extremely 

 difficult to decide whether a given parasite should be looked 

 upon as a HEemollagellate or a Htemosporidian, and, if so, 

 where to draw the dividing line. The writer is truly thankful 

 that he does not feel himself called upon, at present, to 

 attempt to answer such momentous questions. 



adapted ; or that the " cultivated forms " when injected into the Vertebrate 

 host, can give rise to the same phases as those wliich maj' develop after 

 natural infection (see also below, p. 301). 



