| At the apical end of the testes, stem cells divide to produce a spermatogonial cell that undergoes four rounds of mitosis to produce 16 primary spermatocytes. |
| A maximum of 50 offspring were tested from each ENU-treated male to prevent the recovery of identical mutations from the limited population of spermatogonial stem cells. |
| Spermatogonial differentiation lasts 12 days in rats and 16 days in humans, and development of spermatocytes requires 14 days in rats and 25 days in humans. |
| The repopulation index is the percentage of tubules populated with germ cells that had clearly reached the intermediate spermatogonial stage or later. |
| In addition, the testes contained highly refractile cysts that most likely represent degenerating cysts of spermatogonial cells. |
