1. The Ashida R. strain of the small race of the striated spinous loach, Cobitis taenia striata Ikeda, was crossed with the sympatric and allopatric strains of the middle race of the same subspecies. The two kinds of hybrids were compared in terms of male sterility and hybrid breakdown.
2. Both F₁ males derived from the crosses between sympatric races and those from the crosses between allopatric ones are almost completely sterile. There was scarcely any remarkable difference in abnormality of the spermatogenesis between the two kinds of F₁ males.
3. Both RF₁ hybrids derived from the crosses between sympatric races and those from the crosses between allopatric ones partially showed inviability. Any significant difference in degree of inviability was scarcely found between the two kinds of RF₁ hybrids.
4. As far as the present study is concerned, it may be concluded that there is scarcely any positive evidence for the existence of especially strengthened hybrid sterility and hybrid breakdown in the contact regions of the two races.

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Recombination analysis between H and Kp, two genes of the E-pseudoallelic gene group has been reported in another paper.2) The present paper deals with the relationship of the lethality of the recombinants to environmental conditions.
The hatching ability of the eggs of genotype HKp/++ incubated under favorable conditions, for example at a temperature of 23-25°C and 75-80% humidity in the incubation room are shown in Tables 1-2. The mean hatching rate was 79.0% in the cross +×HKp/++ and 83.6% in the reciprocal cross. According to the survey of the hatched larvae the number of the HKp heterozygotes is less than that of normal larvae. In both crosses, +×HKp/++ and HKp/++×+, normal and HKp heterozygous larvae segregated in the ratio 1.5:1.
On the contrary, under less favorable conditions, for example at a high temperature of 27-28°C and low humidity of 50-60% in the thermostat, the same eggs showed a low hatching ability as shown in Tables 3-4, i. e. the mean hatching rate was 58.2% in the cross +×HKp/++ and 51.5% in the reciprocal.
The phenotypic segregation of the hatched larvae is represented in Tables 5-6. In the segregation of both crosses, +×HKp/++ and HKp/++×+, the number of larvae heterozygous for HKp is too small in proportion to the normals. Normal and heterozygous larvae segregated in the ratio 2.9:1 in the former and 7.4:1 in the latter cross.
Theoretically speaking, when the normals are backcrossed to the heterozygotes the two types of larvae should be segregated in the ratio 1:1. The fact that the heterozygous larvae are always fewer than the normals can be explained by the lethal action of the genetic constitution HKp/++ which affects the embryonal stage. We can find many dead eggs produced in each of the batches of Tables 1-4. Probably a major part of the individuals found dead within the eggs may be regarded as HKp heterozygotes. It is clear from the results mentioned above that this lethal action affects the larvae more severely under unfavorable than favorable conditions.
However, some batches showed an abnormal segregation in which the number of the larvae of genotype HKp/++ was by far smaller than that of the normals, even if the individuals within all dead eggs were regarded as HKp heterozygotes. Studies on the cause of this abnormal segregation are now under way.

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1. Loss and variation of antigenic substance (especially blood group substance). There is a close relation between somatic antigen and blood group substance. For examples, antigen 5 of Salmonella B group is nearly the same substance with Forssman antigen (F, FA), antigen 13 of Salmonella G group and Paracolon with O (H) substance, antigen 6 of Escherichia coli O group and antigen 40 of Salmonella with A substance. Serial subculture of these organisms in media respectively containing anti-5, anti- 13 and anti-40 sera produces strains which have lost antigen 5 (F, FA), 13 (O) and 40 (A), respectively. In S→R variation of these organisms, group substances which are present in S form strains are lost with the advance of the process, and replaced by the ones specific to R form strains, which are also lost in the end.
2. Antigenic transformation. As the factor of antigenic transformation, bacteriophage is known besides DNA such as found in Diplococcus pneumoniae. In Salmonella E group, subgroup E₂ which have antigen 3, 15 are lysogenic strains, and E₁ which have antigen 3, 10 are sensitive strains. E₁ strains, when infected with phage derived from R₂ strains, gain antigen 3, 15 by transformation; and E₂ strains, when cultured in a medium containing phage antiserum, lose the prophage and gain antigen 3, 10 of E₁. Subsequently, this epsilon phage as a prophage is considered to take a definite site of the chromosome in bacterial cells of E₂ subgroup and to form a gene-like unit related to the production of antigen 15. When subgroup E₄ strains which have antigen 1, 3, 19 are infected with this phage and become lysogenic, they turn into strains having antigen 1, 3, 15, 19. A similar fact can be seen in the production of antigen 1 of Salmonella B, A and D groups, namely, lysogenic strains infected with iota phage produce antigen 1.
3. Transformation and transduction. The epsilon phage derived from subgroup E₂ of Salmonella E group not only acts as an antigen transforming factor against sensitive E₁ strains but also transduces genetic characters such as drug resistance, suger fermentation, nutritional factor, flagellar antigen etc. Subsequently, one of these characters is transduced into some of strains which have their antigens transformed. But when S. macallen of E₁ subgroup as a sensitive strain is acted upon by the phage, the transduction takes place but not the antigenic transformation. This indicates that, different from the case of the antigenic transformation, it is not necessary for a sensitive strain to turn lysogenic in order that the transduction takes place into this strain.
4. Inheritance of antigen in microorganisms. When genetic recombination takes place between biochemical mutant W-1177 of Escherichia coli K-12 by Lederberg and Escherichia coli C₂ whose antigen is slightly different from that of W-1177, some of the daughter strains have antigen from either one of the parents, and the other have antigen from both parents.

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1. A natural hybrid Paraixeris denticulate×Crepidiastrum platyphyllum is similar to the artificial hybrid of the same combination.
2. The mode of pairing in these hybrids are characterized by having 5 bivalents regularly, in spite of the morphological dissimilarity of the parental chromosomes. The progeny having aberrant combinations of chromosomes is apt to have 5 bivalents at metaphase, although at earlier stages fewer configurations with multivalents are observed. Separations of chromosome parings in later stages are thought to ocurr at the points of the residual paring.
3. As to the possibility for a natural hybrid to be able to begin a starting line of a new species, the present intergeneric hybrids serve as an example of an occurrance of a new type, since the parental characters are more dissimilar than in ordinary interspecific hybrids.
4. The hybrid Paraixeris denticulata (n=5)×Lactuca squarrosa (n=9) has not 14 chromosomes as expected from the parental chromosomes, but has 10-14. And the majority of the cells have 12 chromosomes. This condition is observed in all the 9 individuals studied.
5. The fragmentation and the elimination are observed in the other hybrids, Paraixeris denticulate ×Crepidiastrum Keiskeanum, Crepidiastrum platyphyllum×Lactuca squarrosa. The eliminated chromosomes seem to be the paternal ones.
6. Also in the natural hybrid, these fragmentation and elimination of the chromosomes are observed.
7. Some natural hybrid populations consist of old hybrids with the fertilities of more than 90%, and other populations consist of recent hybrids with the fertility of some 20%.

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