The ultrastructure of endogenous stages of Cryptosporidium muris in the stomach of laboratory mice was studied by transmission electron microscopy. Electron microscopy showed the various developmental stages as free in the gastric gland lumina and attached to the mucus cells. The changes in organelle composition and structure of various stages from the sporozoite to young trophozoites and matured oocysts were demonstrated in detail. Two types of the meront were discriminated. The finding of a microgamete on the parasitophorous vacuolar membrane surrounded a macrogamont was interesting for the stage of fertilization in C. muris. Types 1 and 2 wall-forming bodies were present in fertilized macrogamete or zygote. During sequential development of the endogenous stages, the zygote was separated from the attachment organelle by the clefts, the sporogony process simultaneously appeared when the wall formation progressed, and the sporoblasts were enveloped by budding from the sporont. As a result, thick and thin walled oocysts were found in the parasitophorous vacuole. The interaction of C. muris to mucus cells were quite different from those of other protozoans including Crytosporidium parvum. Each developmental stages of the parasite contained a unique "attachment organelle" which is characteristic of the base of their parasitophorous vacuole. This organelle consisted of a well-developed feeder organelle and the filamentous process. In the free stage of the parasite, it was observed that the zoites developed a surface membrane complex. It was thought that this membrane complex is involved in the building of the attachment organelle.

The ultrastructure of endogenous stages of Cryptosporidium muris in the stomach of laboratory mice was studied by transmission electron microscopy. Electron microscopy showed the various developmental stages as free in the gastric gland lumina and attached to the mucus cells. The changes in organelle composition and structure of various stages from the sporozoite to young trophozoites and matured oocysts were demonstrated in detail. Two types of the meront were discriminated. The finding of a microgamete on the parasitophorous vacuolar membrane surrounded a macrogamont was interesting for the stage of fertilization in C. muris. Types 1 and 2 wall-forming bodies were present in fertilized macrogamete or zygote. During sequential development of the endogenous stages, the zygote was separated from the attachment organelle by the clefts, the sporogony process simultaneously appeared when the wall formation progressed, and the sporoblasts were enveloped by budding from the sporont. As a result, thick and thin walled oocysts were found in the parasitophorous vacuole. The interaction of C. muris to mucus cells were quite different from those of other protozoans including Crytosporidium parvum. Each developmental stages of the parasite contained a unique "attachment organelle" which is characteristic of the base of their parasitophorous vacuole. This organelle consisted of a well-developed feeder organelle and the filamentous process. In the free stage of the parasite, it was observed that the zoites developed a surface membrane complex. It was thought that this membrane complex is involved in the building of the attachment organelle.