The present work is concerned with the gonadal development, oogenesis and fertilization of the multiply tetraploid allogynogenetic silver crucian carp which was found in the artificial breeding population of the Carassius auratus gibellio (♀) * Cyrpinus carpio red variety (♂). On the basis of the material so far, we primarily explored the cytological characteristics of the process of gonadal development and oocyte maturation in tetraploid fishes, and found that the multiply tetraploid allogynogenetic silver crucian carp could develop in two different modes. In one hand, It has been established by our observation that the haploid genome of red carp of multiply tetraploid allogynogenetic silver crucian carp could take part in the process of oogenesis coordinatly. 1) About half of the total oogonia, could increase by normal mitosis with a dipolar spindle and their nuclear material could not be excluded out. This result proved that the red carp genome could coordinatly take part in the cell proliferation in these oogonia. 2) The chromosomal behaviors in oocyte of multiply tetraploid allogynogenetic silver crucian carp is identical with that of the crucian carp: the chromosomes divided into some groups at the stage of monaster of maturation and polyaster of maturation, and maintained the oocyte's chromosomal ploidy with 4n by forming a tripolar spindle and inhibiting the first meiosis. These facts showed that the multiply tetraploid allogynogenetic silver crucian carp stabilized the oocyte maturation mechanism of gynogenetic fishes although the haploid genome from red carp was included in. In the other hand, unusual effects of the genome of red carp were observed: 1) About half of the total of oogonia are sterility by condensation of the nuclear hromatin, and a pattern that chromosomes divided into three groups at the anaphase was found; There are more small aster appeared in the polyaster of maturation of the multiply tetraploid allogynogenetic silver crucian carp than that of the crucian carp, and no rules could be found in both of the distribution of chromosomes and the relationship among the small aster. Otherwise, the polyaster of maturation or dipolar spindle appeared in abnormal position in a few ova. These facts reflected the effects of the red carp genome in the multiplication and maturation of germ cell of the multiply tetraploid allogynogenetic silver crucian carp. 2) Four forms occurred in the gonads of mature individuals: the first is completely fertile female; The second is hermaphrodite, some of them, both of the ovary and testes can be found in the same individual and the others should be confirmed by cytological observation. The third, no gonad in the body of these individuls. The fourth, abnormally developed male, cannot produce mature spermatozoa and is completely sterile. Moreover, on some mature eggs (about 35% of the total) from one individual which we observed, no micropylar apparatus was found in the chorion, and some another egs (about 1.4% of the total) have two micropylar apparatus on each one. It prompted the unusual effects of red carp genome in sex differantiation and development of micropylar cell of the multiply tetraploid allogygenetic silver crucian carp. The development process of two groups, multiple tetraploid allogynogenetic silver crucian carp (♀) * crucian carp (♂) and multiple tetraploid allogynogenetic silver rucian carp (♀) * red carp (♂), were observed. It was found that, in the 2nd group. the sperms of the red arp could not decondense and transform into a male pronucleus after having penetrated into the ovum of the multiple tetraploid allogynogenetic silver crucian carp. That is a typical process of the allogynogenesis. But, in the first group, the sperms of crucian carp have general process of decondensation, formation of pronucleus and conjoint with the female pronucleus. It is so similar to the process of the amphimixis that we call it pseudoamphimixis temporarily. Moreover in the first group, it has been found in most sections that some of chromosomes had been excluded outside when most of chromosomes had arranged at the equator of the spindle at medstage of the first cleavage of the fertilized eggs.