TRYPANOSOMA 6l 



bursts out of the remains of the enclosing erythrocyte, and under- 

 goes a series of nuclear changes preparatory to fertilisation. Then 

 a microgamete penetrates the macrogamete, aided by a cone of 

 attraction which is produced on the latter at the spot where the 

 female nucleus lies. The macrogamete thus becomes the ookinet, it 

 assumes an elongated form and becomes motile. When the blood 

 begins to separate within the midgut of the mosquito, the ookinets 

 migrate towards the anterior portion and here give rise to trypano- 

 soma forms, both sexual and asexual. The asexual and female 

 forms multiply by longitudinal division as in the blood of the 

 bird, the male forms by multiple division. The small division 

 forms attach themselves to the epithelial cells of the midgut by 

 means of their flagella, which become short clinging structures. 

 The attachment of the parasites coincides with the end of diges- 

 tion when the midgut remains empty. Should the mosquito feed 

 a second time, the parasites again become motile. Some of the 

 resting parasites penetrate between the cells or even between the 

 cells and the tunica elastico-muscularis . Usually in these situa- 

 tions they become globular and their flagella disappear altogether. 

 When the latter forms again become free, they develop once more 

 their flagella from the blepharoplasts. The female forms may 

 grow to about three times the size of the asexual ones and 

 become laden with reserve material. They seem unable to multiply 

 by longitudinal division and can only accomplish sluggish con- 

 traction movements. They are no longer capable of transforming 

 themselves into trypanosomes. These gregarine-like resting forms 

 of female trypanosomes have a remarkable power of withstanding 

 adverse conditions. When the mosquitoes after the first meal 

 are obliged to fast for a long period, the asexual and male forms 

 die off, but the female forms persist, they lie between the epi- 

 thelium and the tunica elastico-muscularis, and greatly resemble the 

 zygotes of malaria parasites, although lacking in pigment. f These 

 forms lose entirely their flagellum, the blepharoplast lies close to 

 the nucleus, the reserve material is gradually used up, and large 

 vacuoles appear in the plasma. If, after a long fast, the mosquito 

 again feeds, the female forms which have survived reproduce the 

 asexual forms by parthenogenesis (a kind of auto-fertilisation). 



The zygotes which give rise to male forms are somewhat 

 smaller than those which develop into female forms, their plasma 

 is almost hyaline and coarsely vacuolar, the nucleus is relatively 

 larger, and is very rich in chromatin. Having undergone certain 

 nuclear changes the microgametocyte becomes globular and breaks 



