Ultrastructural observations on macrogametogenesis and the structure of the macrogamete of Isospora felis.

The ultrastructural changes occurring during macrogametogenes of Isospora felis were studied in the small intestine of the cat at 8 and 9 days post-infection. The parasites were situated in parasitophorous vacuoles within the host epithelial cells. The early macrogamont could be identified by its ellipsoidal shape and by the presence of a large nucleus with a distinct nucleolus. Throughout the development of the macrogamont the organism remained limited by a pellicle. At an early stage of macrogametogenesis the formation of the wall-forming bodies of types I and II (WFB I and WFB II) was initiated simultaneously. The formation of the WFB I appeared to involve the rough endoplasmic reticulum (rER) and the Golgi bodies, whereas the WFB II developed within cisternae of the rER. Early in the developmental process vacuoles were observed which budded off from the nucleus and formed multimembranous vacuoles. During gametogenesis both lipid globules and polysaccharide granules developed within the cytoplasm. The mature macrogamete was spherical in appearance and was limited by a pellicle. It possessed a large nucleus with a nucleolus and the cytoplasm was filled with numerous WFB I, WFB II, lipid globules and polysaccharide granules. A few multimembranous vacuoles were also present together with canaliculi, mitochondria, Golgi bodies and some rER.