Fig. 3.

Electron micrographs illustrating changes occurring during sporulation. (a) Section through an unsporulated oocyst (zero hour) showing the central nucleus (N) with cytoplasm containing a number of polysaccharide granules (PG) and lipid droplets (L). Bar = 1 µm. (b) Section through the two secondary sporoblasts. N, nucleus; L, lipid droplet; PG, polysaccharide granule. Bar = 1 µm. (c) Early development of the sporocyst showing the elongated appearance with a nucleus (N) located at either end of the sporocyst and the cytoplasm containing polysaccharide granules (PG) and lipid droplets (L). Bar = 1 µm. (d) Cross-section through the sporocyst wall which consists of a thin, continuous outer layer and an inner layer consisting of four plates. There is a swelling of the plates of the inner layer at the junction where they are joined by an intermediate strip (IS) of material. Bar = 100 nm.(e) Enlargement of part of a sporoblast showing the nucleus (N) and the two dense plaques (arrows) representing the initiation of daughter formation. Bar = 1 µm. (f) Advanced stage of sporozoite formation (SP) showing the nucleus becoming enclosed by the inner membrane complex of the daughters. The junction between the four plates of the sporocyst wall can be seen (arrows). Bar = 1 µm. (g) Scanning electron micrograph illustrating the raised junctions between the plates (arrows). Bar = 1 µm. The techniques used and images are from Ferguson et al., 1978, Ferguson et al., 1979a, Ferguson et al., 1979b, Ferguson et al., 1979c with permission.