Relation between fertilization rate and penetration of eggs by supplementary spermatozoa in different mouse strains and crosses

Summary. The percentage of unfertilized eggs, and of fertilized eggs containing supplementary spermatozoa under the zona pellucida, was estimated on the day after copulation in the diallele crosses involving inbred strains: CBA, C57, KE and one outbred strain. A significant correlation between the two investigated characters was found (r = 0\m=.\84).The significant influence of the strain both of the male and of the female was found by the heterogeneity test. CBA, outbred, C57 and KE males yielded 0, 3, 5 and 15 % ofunfertilized ova, and 14, 18, 27 and 35% ofova containing supplementary spermatozoa, respectively. CBA females showed the lowest figures for both characters, and KE and outbred ones the highest. The evidence seems to suggest that penetration of the vitellus is affected in KE mice because of some failure to interact on the part of both the spermatozoa and the ova belonging to this strain