Muscular samples of the oesophagus and diaphragm of 335 sheep collected from the slaughterhouse of El Harrach were analyzed by the histopathological method to describe the morphology of two species of Sarcocystis: S. arieticanis and S. tenella. The cysts were counted and measured with a micrometer for their dimensions. A total of 895 cysts were measured. The width, length, shape index (length/width), the thickness of the wall and the length of the projections were recorded. The thick-walled cysts of S. tenella were 10—450 μm long (the mean ± SD value was 50.35 μm ± 1.380) and 1—110 μm (the mean ± SD value was 27.51 μm ± 0.533) wide. The cyst walls were 0.5—4 μm thick (the mean ± SD value was 1.547 μm ± 0.020) and provided with radial striations. The shape index was 1—14 μm (the mean ± SD value was 1.93 ± 0.045). While in the S. arieticanis, the cyst wall was thin and had long hair-like protrusions, the cysts measured 8—780 μm (the mean ± SD value was 123.13 μm ± 12.799) in length and 5—100 μm (the mean ± SD value was 37.00 μm ± 1.68) in width. The hair-like protrusions reached a length of 3—14 μm (the mean ± SD value was 5.428 ± 0.353) and the shape index was 1—17 μm (the mean ± SD value was 3.10 ± 0.281). For the length, the width and the shape index, the differences were statistically significant between thin-walled cysts and thick-walled cysts. The general structural features of the cysts, previously described by other authors, were confirmed.
