248 Development of Trypanosoma garnbiense in Glossina palpalis. 



taken the place of conjugation. This hypothesis would explain the labile 

 characters and the extraordinary merging of species in the trypanosome group, 

 but it is obviously open to much criticism on the score of its speculative 

 nature. Further, such a conception stands only so long as no sound evidence 

 of conjugation in any trypanosome cycle is to hand. 



In any case it seems clear that the cycle in the fly as a whole, whether 

 conjugation actually occurs or not, has much of the. biological significance of 

 that process. This conception is of some importance to workers dealing with 

 laboratory strains passed directly for long periods without reference to the 

 intermediate host. 



It might be suggested that the fluctuation in the infectivity of the blood of 

 the vertebrate, on which these experiments have laid particular stress, is due 

 to the coming and going of sexual forms in the peripheral blood. The 

 microscopic appearances in the vertebrate have not as yet been sufficiently 

 closely correlated with the infected periods to permit of any statement as to 

 whether there is a morphological distinction in the individuals at different 

 times. 



This paper does not deal with the morphological aspect, but I should like to 

 deprecate the rash use of the terms male and female to describe slender and broad 

 trypanosomes. In T. garnbiense cycles, in the glossina, very slender elongated 

 forms are produced from the broad forms, as in most other trypanosome life- 

 histories ; they are naturally present together in the posterior part of the gut, 

 but the former are destined to pass forwards and form the overwhelming 

 majority of the individuals in the proventriculus and thoracic intestine. The 

 terms male and female are gratuitously misleading until the individuals have 

 been shown to have a sexual connection. 



Such a use of language encourages an undue bias in the mind of the 

 observer, and, while I am far from denying the possible and even probable 

 occurrence of a sexual process, it is obviously an unscientific procedure to 

 select the individuals a priori by the casual method of analogy, an analogy, 

 moreover, not even drawn from the same class of the protozoa. 



