Studies by electron microscopy of the giant forms of some African and South American trypanosomes found other than within their mammalian host.

Giant multinucleate cyst forms of 3 brucei group trypanosomes and 2 South American species were found in culture systems and within the insect host cells by electron microscopy; the African stocks within the tsetse mid-gut cells, an unidentified Brazilian trypanosome within the bug's gut cells and Trypanosoma rangeli within the muscle layers surrounding the bug's salivary gland. The various forms found were similar in that they contained varying numbers of large vacuoles, usually lined by subpellicular tubules into which appeared to bud the various organelles seen in normal trypanosomes and which were produced in considerable numbers within the body of these giant forms. These large vacuoles were seen opening to the exterior and liberating what could be small new forms. Sometimes direct budding of new small forms was observed directly from the pellicle of the giant form. The possibility that these giant forms may arise from some type of fusing of individual trypanosomes, that they may perhaps give rise to new individuals and that such a process might provide a mechanism for genetic exchange is discussed.