Multiplication of Trypanosoma pacifica was common in the fish host from observations of live flagellates and Giemsa-stained blood smears. Multiplication began with the elongation of the kinetoplast, thickening of the posterior portion of the body, and appearance of a new flagellum near the kinetoplast. The new flagellum was very rigid when less than 3 μm in length, but it became flexible as it elongated. When the new flagellum was approximately 12 μm in length, cell division began and the kinetoplast also began to divide. The timing of nuclear division was variable. Generally, it did not occur until division of the kinetoplast had begun, but occasionally binucleate individuals were observed before cell or kinetoplast division was apparent. As division continued, 1 nucleus migrated past the dividing kinetoplast into the future daughter trypanosome. Finally, the kinetoplast completed division and the trypanosomes separated. Cell division was unequal, with the daughter trypanosome being smaller than the parent and with a more weakly developed undulating membrane.

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