Abstract
Body and adrenal weights, and histology of the adrenal cortex were examined in the chamois-coloured mastomys (Praomys coucha) at inbred generations 3 to 10. Body and adrenal weights were consistently larger in males than in females, although the adrenal to body weight ratios tended to be lower before 50 days of age and were clearly higher after. Distinct sex differences were found in the adrenal cortex. The whole cortex and the zona reticularis were thicker in males and the zona reticularis became thicker in males, but thinner in females with age. The border zone characteristics of females of the wild-coloured mastomys strain, was not formed in the chamois-coloured strain. This was a very unique, interesting strain difference. Comparative studies of both strains may contribute to elucidation of the mechanism of border zone formation in the mastomys adrenal cortex.