The total Leydig cell volume of the testis in some common mammals.

Total Leydig cell volume has been quantitatively determined by a histometric point-counting method in six common mammals, including man. Although the size of the testis has increased from 1.3 +/- 0.1 ml in the rat to 19.8 +/- 6.9 ml in the buffalo, the composition has remained fairly constant with the Leydig cells making up 9--16% of the testicular volume. In absolute terms, the Total Leydig Volume has increased progressively with body size, from 0.11 +/- 0.02 ml/testis in rat to 2.44 +/- 0.64 ml/testis in buffalo, the value for man being 2.21 +/- 0.40 ml/testis. The significance of these findings, from the point of view of the comparative physiology of male reproduction, has been discussed.