340 FAMILY: TRYPANOSOMID/E 



are included in the complicated descriptions of the latter writer. The 

 observations, or more correctly the deductions, made by him were un- 

 doubtedly the outcome of a theoretical bias, and cannot be accepted. 

 Influenced by these statements, numerous observers, without any evidence 

 whatever, have described as male and female flagellates the narrow and 

 broad forms which occur in almost every infection. The figured stages 

 of conjugation can always be interpreted as the final stages of a division 

 in which a narrow form, the supposed male, is separating from a broader 

 one, the supposed female. The instance recently described by Fran9a 

 (1920cf) for Phytomonas davidi is unconvincing, as the forms figured can 

 easily be explained as dividing individuals or the casual association of 

 two flagellates. 



As regards the pathogenic trypanosomes. Woodcock and Lapage (1915) 

 go to the other extreme, and suggest the complete loss of syngamy in this 

 group. It is quite possible that a sexual process takes place in association 

 with the development of trypanosomes in their invertebrate hosts, but the 

 most careful observations, such as those of Robertson (1913) on the develop- 

 ment of T. gambiense in tsetse flies, and of Minchin and Thomson (1915) 

 on T. lewisi in the flea, have failed to reveal one, though the possibility 

 of its having escaped detection is admitted. In order to demonstrate a 

 sexual process, something more than a casual association of two unequal 

 forms in stained films is necessary. The formation of "latent bodies," 

 as described by Breinl and Moore, and referred to above, was supposed by 

 them, without any real evidence, to depend on a fusion of the kinetoplast 

 and nucleus, and to represent a process of self-fertilization or autogamy. 

 Roubaud (1911c, 19126) noted that in certain insect flagellates, when 

 they became leishmania forms in the hind-gut in preparation for encyst- 

 ment, the kinetoplast approached the nucleus. He concluded that actual 

 fusion of the two sometimes took place, and that a process of autogamy 

 was represented. It is very doubtful if any fusion occurs, as the dis- 

 turbing effect of drying the parasites on films so obscures the true nuclear 

 structure that it is impossible to be certain that any apparent fusion of 

 two closely applied bodies is not merely artificial. Quite apart from the 

 defects due to drying, it often happens that the kinetoplast lies over the 

 nucleus, and it becomes impossible to distinguish the two as separate 

 bodies in such minute organisms. Even if such a fusion as that described 

 takes place, there is no evidence that it represents syngamy in any form. 



It is clearly evident that, of the numerous statements w^hich have been 

 made regarding the occurrence of sexual difierentiation and syngamy 

 amongst the Trypanosomidse, not one has any evidence to support it. 



