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. ヤクシソウとワダンとの雑種は自然に存在するヤクシワダンとよばれるものもあるが, 人工的につくつた雑種もだいたいこれと同じものになる.
2. この雑種の減数分裂における対合は特異であり, 染色体形態の異るにもかかわらず, 常に 5_IIがみられる. その子孫においては染色体の配分がいろいろとみだされるが, 中期では5個の Configurationsを示すものがもつとも多く見られた. しかしより早い時期では, Configurations の数の減少, すなわち多価染色体が多く見られた. このようにはじめに結合していて中期に進むにつれて解消するような結合を残余対合 (residual pairing) とよんだ.
3. 自然雑種は新しい種の出発点となり得るかどうかはいろいろの考えがあるが, 属間雑種のように両親の形質が遠いものでは, 二次的安定種がつくられる可能性が示された.
4. ヤクシソウとアキノノゲシとの雑種では染色体数が一定しないで 10～14 のいろいろの数の細胞が一つの根においてもキメラになつているのがみとめられた. しかしその中で12のものが, もつとも多く, しかも得られた9個体において, このことは常に一定であつた.
5. 同じような染色体の分断消失による減少はヤクシソウとアゼトウナとの雑種, ワダンとアキノノゲシとの雑種においても見出される. しかもいつでも分断消失する染色体は父方のものである.
6. 自然にもこのような雑種がみられるが, アゼトウナ自然集団の中から採集された自然雑種においても同じように染色体の分断消失がみられる.
7. 自然集団の中には 90% 以上の高い稔性のもののみの集団と 20% ぐらいのひくい稔性のものをふくむ集団とがある. 前者は古くできた雑種集団であり, 後者は新しくできた雑種のふくまれる集団であると思われる.

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