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An electron micrograph of a section from the testis of a rat of group II showing hyperchromatic nucleus (N) of the spermatogonic cells (SG) with irregular clumps of heterochromatin (arrow). The cytoplasm contains many distorted mitochondria (crossed arrow). Note the presence of perinuclear haloes (H) and many vacuoles (V) in between the cells (TEM × 3000).
