Abstract: The egg of naturally gynogenetic crucian oarp can inhibit heterologous sperm from transforming into male pronucleus so that ontogenesis is completely controlled by the female nucleus. By removing female nucleus, transferring egg cytoplasm and inseminating the egg after the removal of chorion, the present experiment preliminarily revealed the way the egg inhibits sperm nucleus from transforming into pronucleus. On the basis of the experimental results, a hypothesis of double control is advanced: the gynogenetic egg has primary control and secondiary control over the heterologous sperm. The primary control may be accomplished by a certain special inhibitor located in the passage where the sperm enters the egg. The secondary control may be due to the lack of an unknown substance generally existing in the egg cytoplasm of amphimictic fish to promote the formation of male pronucleus.