Changes in the diameter of Isospora lacazei (Labbé, 1893) oocysts in the house sparrow, Passer domesticus (L.).

Differences in the diameter of Isospora lacazei oocysts were found to be dependent on diet and other factors. House sparrows which were given animal products as food (hard boiled eggs) excreted with their faeces coccidia oocysts, which were larger than when they were fed grain. The results indicate a need to verify the divisions of the systematics of Isospora lacazei.