706 H. M. WOODCOCK. 



T. mesuili with most of those of T. avium, I am 

 strongly inclined to say that the cultural development of the 

 former parasites was not proceeding so successfully — at any 

 rate, when the preparations concerned were made — as that of 

 the last-named species. 



Slight differences in the constitution of the medium may 

 certainly influence the rapidity of growth of these cultural 

 forms, as I have stated above, and probably also, to a certain 

 extent, the manner of their development. Further, it is 

 quite likely that different species of trypanosomes, when 

 cultivated in the same medium, may also differ in their rate 

 of growth and in the development of the different types of 

 form. Hence, I think we may agree with Novy and McNeal, 

 although on quite different grounds, that the parasites which 

 they name T. laverani and mesnili are at any i*ate 

 different from the other (T. avium). Moreover, it may 

 be reasonably inferred that under slightly different condi- 

 tions — in one way or another — of the medium, these forms 

 would also develop a trypaniform phase. For it will be seen 

 from the subsequent context of this paper that there is every 

 reason to suppose such a phase is of regular occurrence at 

 some period in the development of a trypanosome outside the 

 vertebrate host. As a matter of fact, T. laverani itself 

 appears to be very closely allied to the trypanosome with 

 which I have been working. 



The only other paper dealing with cultural forms, to which 

 I need refer is a note by Thomson (35), on the cultivation of 

 trypanosome (probably T. danilewskyi), from the goldfish, 

 which gives instructive indications of the course of develop- 

 ment of that parasite in cultui-es. It is most interesting to 

 find that there is a general resemblance between the course 

 of events in the case of that piscine form, as outlined by 

 Thomson, and in the avian parasites discussed above. 

 Thomson does not describe any developmental forms occurring 

 earlier than the seventh day. By this time the parasites are 

 in a phase corresponding to my accentuated tr^^panomonad 

 type ; and division by a quite similar method of unequal 



