Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The study was undertaken with the purpose of redescribing the life history stages of E. labbeana and working out the histochemistry of different stages. Freshly discharged oocysts were of two sizes, large and small. Each oocyst possessed an outer transparent membrane, a thick intermediate membrane, and a thin inner membrane. The cytoplasm was in a state of flow and the nucleus appeared as a halo. Oocysts with incompletely formed walls and degenerate oocysts were also found to be shed along with mature oocysts. Biometrical studies indicated that the "ideal" size of the oocyst was 19.2u ± 0.27u x 17 . 5u ± 0.21u. There was no special difference in the size of the oocyst early and late in the patent period. Observation of sporogony at room temperature revealed that the first change in freshly discharged oocysts took place after 9 to 9 1/2 hours when protoplasm was withdrawn to a globular form. One to three polar bodies arose from any point. After 20 to 21 1/2 hours sporoblasts appeared abruptly. The first division was longitudinal and the second transverse. At about 33 hours sporoblasts changed to sporocysts. At about 59 hours the cytoplasm of sporocysts divided to form 5 refractile globules. The sporocyst had a double wall, the inner one reaching up to the base of the Stieda body. Two refractile globules (future sporozoites) were at either end. The average length and width of the sporocyst was 12.4u ± 0.34u X 6.4u ± 0.08u.[TRUNCATED] / 2031-01-01