SPERM PENETRATION AND THE FORMATION OF A FERTILIZATION CONE IN THE COMMON CARP EGG*

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Abstract
Sperm penetration and the formation of a fertilization cone in the micropylar canal of the common carp egg were examined by EM. The overwhelming majority of inseminated eggs fixed without immersion in fresh water showed that the 1st spermatozoon penetrated into the ooplasm before the cortical reaction occurred and, in many cases, formed a fertilization cone to plug the micropylar canal. At this stage the sperm head was usually located at the base of the cone, and the tail part did not participate in the cone formation. Inseminated eggs fixed soon after immersion in fresh water showed that the elevation of the fertilization membrane, and the simultaneous recession of the fertilization cone, often permitted the penetration of a few supernumerary spermatozoa into the perivitelline space near the micropylar canal; polyspermic fertilization, however, was never observed. The mechanism of the block to polyspermy in the egg of the common carp is discussed in connection with the fertilization cone.