Fine structure of the oocyst wall of Eimeria nieschulzi.

Oocysts of Eimeria nieschulzi from the laboratory rat, Rattus norvegicus, were studied by scanning and transmission electron microscopy. Oocysts had a rough outer wall with apparent random depressions. The oocyst wall is composed of 2 layers: an osmiophilic outer layer consisting of a rough external and smooth internal surface, and a relatively thick, electron-lucent inner layer. The outer layer is composed of a dense, coarsely granular matrix. The inner layer consists of homogenous fine granular material interspersed with coarse osmiophilic granules and contains one closely applied membrane on the outermost surface. Several raised lenticular areas are seen on the coarse outer surface of the inner layer. These layers are 102 (75-128) and 176 (135-204) nm thick, respectively. The sporocyst wall is thin, consisting of 3 to 4 unit membranes, and measures (18-34) nm thick.