| Abstract: | An ultrastructural study was made of the spore envelope during development in the microsporidan, Thelohania bracteata. The frozen-etched outer (convex) face of the relatively thin spore coat in the earliest immature stage of development has a granular structure in regular array. The inner (concave) face bears particles as well as depressions arranged in a net-like pattern. The mature spore coat has a substructure of numerous microfibers, ～8 nm in diameter, arranged in a matrix and forming thin layers which run parallel to the spore surface. The mature spore coat possesses both outer and inner limiting layers. The outer (convex) face of the outer limiting layer is granular. The convex face of inner limiting layer bears many particles as well as many long, narrow depressions. The concave face of the inner limiting layer carries many stud-like projections, ～40 nm long and 30 nm high, which are complementary to the depressions observed on the convex face. In addition, the concave face has subunits ～15 nm in diameter, apparently arranged in a hexagonal pattern with a center to center distance of ～18 nm. The change in size of these projections, depressions, and subunits presumably is related to spore maturation. |
