Abstract: Cytological study on the fertilization with sperms of gynogenetic crucian carp and eggs of amphimietie common carp has been made in order to reveal the mechanism which leads to the death of the hybrid embryos. It showed that the sperms were able to transform into male pronuclei and fuse with female pronuclei, so that the zygotic nuclei were formed. However, after the beginning of cleavage, some unusual phenomena, such as the elimination of chromosomes, the formation of multiple spindles and the asynchronous division of the two blastomeres of the same egg, were observed. From these results, the authors are preliminarily of the opinion that, between gynogenetic crucian carp and other fishes, there exists a certain chromosome incompatibility which leads to the repelling of chromosomes in the hydrid embryonic cells. probably, this reflects the unique genetic background of the chromosome complement of gynogenetic crucian carp.