Superpregnancy in the mouse. 1. Implantation and foetal mortality after induced superovulation in females of various ages

In 1927 Engle used pituitary implants to induce ovulation and oestrus in adult female mice mated to fertile males. At post mortem examination of their uteri 9-10 days later he found large numbers of embryos, ranging from 19 to 29. He did not follow the fate of such embryos into later pregnancy. But his observatio