Notes on the Life-History of Trypanosoma gambiense, etc. 67 



No sexual differentiation of any kind is to be observed among the blood- 

 types. The differentiation into long and short forms is a phenomenon of 

 growth and division, and is not an expression of sex. 



A wet fixation of the blood-films in corrosive alcohol, and subsequent 

 staining and mounting without drying in air, gives the nuclear picture shown 

 in figs. 25 and 26. This is in accord with the observations upon live 

 specimens, and is identical with that found in other trypanosomes studied 

 by similar methods. A division-stage is shown in fig. 27. 



II. Exogenous Cycle in the Fly. 



A great deal of information can be obtained from a close study of the 

 conditions in the early days of the cycle as to what are the factors 

 inhibiting the development of the trypanosomes in the Glossina. I do not, 

 however, propose to discuss these here ; suffice it for my present purpose to 

 take those cases in which trypanosomes have established themselves, and to 

 trace the usual development. 



While the series of changes undergone in the Glossina up to the time 

 when it becomes infective to clean vertebrates is very definite and constant, 

 nevertheless, the duration in time of this cycle varies in different cases 

 within the limits of more than a fortnight. This must naturally be borne in 

 mind when considering the successive stages in the cycle of any given fly. 



The trypanosomes never attach themselves while in the gut, nor do they 

 ever disappear from this situation at any period ; the development occurs 

 free in the lumen of the alimentary canal from the very start. At no period 

 do the parasites enter the body-cells of the host, nor do they penetrate 

 through the gut-wall into the body cavity. 



The earliest processes that take place in the fly are characterised by a 

 slight and rather indefinite change of form (figs. 1 and 2). Broad, slender 

 and degenerating specimens are all present, but only the broader types are 

 ever found in division at this early stage. These first divisions (figs. 3 and 5) 

 are remarkable in that they show a suppressed crithidial phase in the young 

 individual. This disappears before the separation of the two products (fig. 4). 

 The peculiarity just noticed does not occur in the later divisions, and has 

 never been observed after the 10th day. The gut stages do not show any 

 other crithidial phase. The trypanosomes usually start developing in the 

 middle or posterior intestine (mid-gut), and by the 7th to 10th day there 

 are a large number of trypanosomes present, showing the general features 

 depicted in figs. 6-12. Division goes on rapidly, and the nature of this 

 process is shown in figs. 8-10. 



It will be observed than the granule at the base of the fiaoellum 



