Toxoplasma gondii undergoes schizogony and microgametogony in the epithelial cells of the cat ileum. On the basis of cytoplasmic structures, it is impossible to distinguish between the early stages of these processes but nuclear differentiation appears to have occurred. In the early schizont the chromatin is distributed in small patches throughout the nucleus but in the nucleus of the microgametocyte the chromatin is condensed into a few large areas. In the schizont, the first distinguishing cytoplasmic features are the appearance of the dome‐shaped membranes of the merozoite anlagen. In the schizogonic process, nuclear division precedes merozoite formation which occurs by multiple internal budding in a manner similar to endodyogeny. The appearance of flagella is the first cytoplasmic feature to distinguish the microgametocyte. Microgamete formation is similar to that reported for other coccidian species. The microgamete consists of a dense elongate nucleus anterior to which is a single mitochondrion. The anterior consists of a perforatorium and two flagella between which 4 microtubules run longitudinally.

Of course, mass radiography has widened its scope since its introduction in the early 1940s. It has become a service, a tool for presymptomatic diagnosis. X-ray departments in hospitals are neither meant nor equipped to do this. To destroy such a service without even taking regional differences and problems into consideration is a retrograde step.-I am, etc.,

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Siim, J. Chr. The ultrastructural development of the macrogamete and formation of the oocyst wall of Toxoplasnia gondii. Acta path. microbiol.scand. Sect. B, 83: [491][492][493][494][495][496][497][498][499][500][501][502][503][504][505] 1975.The macrogametes of Toxoplmrna gondii develop within the epithelial cells of the cat ileum. As they develop the nucleus enlarges and dense patches of chromatin which were present in the nucleoplasm, disappear. Polysaccharide granules and lipid globules appear in the cytoplasm and increase in number during development. The wall-forming bodies of Type I (WFB I ) appear before the wall-forming bodies of Type I1 (WFB 11) ; WFB I are smaller, more osmiophilic and more numerous than the WFB 11. The WFB I appear to form from vesicles produced by the smooth endoplasmic reticulum, and the WFB I1 form within the lacunae of the rough endoplasmic reticulum. Double membraned vacuoles appear to form from the nuclear membranes but the function of these is unknown. Throughout development the macrogamete retains a normal pellicle which possesses numerous micropores. The first evidence of oocyst wall formation is the appearance of participate matter in the parasitophorous vacuole which precipitates to form Layer 1 of the oocyst wall. Layers 2 and 3 are unit membranes which form between Layer 1 and the pellicle. During this development the organism has an organelle complement similar to that of the macrogamete. Layers 4 and 5 form between 1,ayer 3 and the pellicle. Layer 4 is osmiophilic and its formation is accompanied by the disappearance of W F B I . Layer 5 is less osmiophilic than Layer 4 and its formation is accompanied by the disappearance of WFB 11.The two innermost layers (Layers 4 & 5 ) in the oocyst wall of Toxoplasma are similar to those found in Irospora spp. and Eimeria spp,. Toxoplasma seems to be unusual in that, firstly, it possesses an additional 3 layers and, secondly, all 5 layers are formed outside the pellicle of the original macrogamete.Prior to 1969, only the exo-enteric stages of Toxoplasma gondii were known. These two stages were found in many mammals and birds and are now known as endozoites and cystozoites (Hoare 1972). Both stages repro-

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