﻿98 Proceedings of the Royal Physical Society. 



due, perhaps, to nutrition — this being apparently borne out 

 by the fact that they are always developed at the middle 

 period of digestion, when the fluid in the intestine is 

 probably most rich in nutritive material. No such table 

 of sizes as that drawn up for T. brucei and T. gamhiense, in 

 Koch's interesting paper ^ for male and female forms, could 

 be made in the case of the trypanosome in Pontoldella. 

 One feels that it is dangerous to settle a point of this kind 

 from analogy with other forms, and at the present state of 

 our knowledge it is better to leave the matter unprejudiced. 

 Of course, one may here be dealing with a continuous series 

 of forms of which the extreme members might be considered 

 respectively male and female, and we might possibly here 

 be confronted with a transition between Isogamy and 

 Heterogamy or — what is perhaps more probable — with a 

 condition of affairs in which only the extreme members 

 of the series proceed to conjugate: that is to say, only 

 those individuals in which the male and female differentia- 

 tions are expressed actually conjugate. Speculation is not, 

 however, of much use until more of the facts are known. 



The only remaining forms to be dealt with are the minute 

 creatures which persist, and which appear to be capable of 

 preserving, the infection in the leech. 



These do not call for special description, as they are 

 simply, as far as I can see, miniature replicas of the larger 

 forms, and seem to grow into small, rather thin trypanosomes, 

 which increase in dimensions as digestion goes on (Figs. 

 60-63). 



There is one phenomenon still to be mentioned before 

 passing to the consideration of division, namely, the tendency 

 of isolated trypanosomes, in almost all the different stages, to 

 return at times to the rounded-off state. I do not know 

 what exactly brings this about. The result, however, is 

 sometimes to very much heighten the extraordinary variety 

 of external shape to be observed in a strong infection during 

 the middle period of digestion. 



^ Koch, "tiber die Unterscheidung der Trypanosomenarten," Sitzher. der 

 k. pr. Akad. d. Wiss, 16th-23th Nov. 1905, page 961. 



