Fig. 19–23.

Reference isolate of B. algerae grown in athymic mice. 19. Infected cell from the tail of the mouse. All parasite stages are present: diplokaryotic proliferative (P) and sporogonic parasite cells, including sporonts (SP), sporoblast (SB), and spore (S) cells in direct contact with cell cytoplasm. Note the difference in cell surface structure between early and late stages. Bar = 1 μm. 20. Proliferative cell with thickened plasmalemma, appendages, and ridges. Bar = 0.5 μm. 21. Elongated proliferative cell (P) with an eccentrically positioned diplokaryon (D). Note the difference in cytoplasmic density between the proliferative and sporont stages (SP). Bar = 1 μm. 22. Two sporoblasts (SB) with homogeneously dense cell surfaces, denser cytoplasm, and the early stages of polar filament formation. Compare with proliferative cell above. Bar = 1 μm. 23. Mature spore with 9–10 coils of the polar filament in a single row. Note the presence of a uniformly dense exospore coat. Bar = 0.5 μm.