Rat eggs were transferred to the oviducts of previously mated rabbits. The purpose of such transfers was to find out whether or not spermatozoa of one species can penetrate through the zona pellucida of another species. Of the 673 rat eggs that were examined, the perivitelline space of one contained a rabbit spermatozoon. Penetration in this single instance seemed to have occurred due to abnormalities in the spermatozoon.
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