E, Hindle and R. C. Lewis 
111 
Fig. 1. Large flagellate form with a well developed undulating membrane. The flattened, 
somewhat leaf-shape of the parasite is well shown at the spirally twisted posterior 
extremity. 
Fig. 2. Form in which the kineto-nucleus is situated rather more anteriorly than 
usual. 
Fig. 3. Large flagellate form with dividing kineto-nucleus. 
Fig. 4. Long slender form with elongated tropho-nucleus. The long flagellum arises 
from a conspicuous end-bead. 
Fig. 5. Flagellate form showing a distinct karyosome inside the tropho-nucleus. 
Figs. 6-11. Various stages in the longitudinal division of CrithkUa. 
Figs. 6, 7. Forms showing commencement of division of kineto-nucleus and end-bead. 
Fig. 8. Large flagellate possessing two kineto-nuclei and dividing end-bead. 
Fig. 9. Small dividing form showing the commencement of the formation of a new 
flagellum from the divided end-bead. 
Fig. 10. Large flagellate form in which both nuclei and end-bead have divided. 
Fig. 11. Commencement of fission at the anterior extremity. 
Fig. 12. Form showing concentration of protoplasm and both nuclei towards the 
posterior extremity. 
Fig. 13. Pre-flagellate stage with dividing kineto-nucleus. 
Fig. 14. Pre-flagellate form in which both nuclei have divided. The end-bead is in process 
of division. 
Fig. 15. Stage in the formation of a cyst. The protoplasm is very dense and contains 
granules. 
Figs. 16, 17. Encysted post-flagellate forms each showing distinct tropho- and kineto- 
nuclei. 
very large and is stained rather faintly, and the kineto-nucleus is also 
large and horse-shoe shaped and is very densely stained; the latter 
may be in process of division. Fig. 14 represents a rather interesting 
form which is at an advanced stage of division. Both nuclei have already 
divided and are situated at opposite sides of the protoplasm, and, in 
addition, the end-bead is clearly seen in process of division. No trace 
of this structure could be found in the other pre-flagellate, or in any of 
the cysts and therefore it seems probable that the end-bead appears 
shortly before the flagellum is formed and disappears in the post- 
flagellate stage, together with the flagellum. 
Flagellate forms. This stage is extremely abundant in the films, 
the flagellates often occurring in large masses apparently as the result 
of rapid multiplication. Many of the parasites are in process of division, 
shown by the appearance of the kineto-nucleus or its associated end- 
bead. The usual variations with regard to size, shape and the relative 
position of the two nuclei are well shown. The tropho-nucleus is 
usually situated about the middle of the cytoplasm (Figs. 1, 3), but the 
kineto-nucleus may vary from a position immediately in front of the 
tropho-nucleus to one half-way between the latter and the anterior 
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