1) This paper deals with the results of crosses among ten species of Rubus, and of observations of genetic characteristics and cytological phenomena of the six F₁-hybrids.
2) The crosses of R. trifidus (2n=14) as the mother with the other diploid species were more successful than the crosses among the other species. And all the crosses of R. hirsutus (2n=14) as the mother failed to give hybrids. All the crosses between the polyploids and the diploids give no hybrid. Hybrids are obtained regardless whether the parents belong to the same subgenera or not.
3) The characteristics of the parental species are inherited to the F₁-hybrids in several distinct behaviours, which may be classified into four types: a) dominant, b) recessive, c) intermediate betwecen the parents, and d) hybrid vigor.
4) In the fertile hybrids, R. trifidus×palmatoides, ribisoideus×palmatoides, ribisoideus ×Fauriei and palmatoides×Fauriei, the most frequent configuration of chromosomes is 7_II at IM. While in the sterile hybrids, R. trifidus×hirsutus and trifidus× ribisoideus, univalents are offen observed at IM. When the univalents appear at IM of the sterile hybrids, the frequencies of occurrence of 6_II+2_I and 5_II+4_I are higher than those of the other configurations. The fertile hybrids have a large amount of normal pollen grains, but the sterile hybrids have less normal grains. The phenomenon of the latter may be due to the irregularities of meiosis.

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Fifth-instar larve with genotypes +/lem^l and lem/lem^l, which had segregated from a cross between +/lem^l and lem/lem^l, were used as material. The ovaries of the larvae of both types were exchanged. Of 630 larvae thus operated upon, only 3 survived and had offspring.
The female moths produced from these larvae were mated with male moths of the genotype lem/lem^l. The eggs laid were incubated and larvae homozygous for lem^l gene were examined.
When the +/lem^l larvae were implanted with ovaries of lem/lem^l, the homozygous lem^l embryos which developed from the transplanted eggs hatched out, as the apparently normal ones do, as black-coloured larvae, but they changed into distinctly yellowish larvae which died immediately after the first moulting.
On the other hand, the lem^l homozygous larvae emerging from eggs laid by the lem/lem^l moth which had received a +/lem^l ovary by transplantation developed into yellowish-brown young larvae, then died within the egg.
From these results it may be concluded that the stage of death of the lethal larvae is not determined by the genotype of the embryo (+/lem^l or lem/lem^l) but by that of the mother's body in which the eggs develop.

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T3 hs phage is a strain of T3 h phage which produces an irregular plaque on E. coli B wild type strain, but the round one on E. coli Bs/3 strain. The experiments reported here is performed to secure the mechanism of irregular plaque formation on E. coli B by this phage. It was concluded that the T3 hs phage is a minute mutant (T3 hm) which produces a minute plaque only on E. coli B and a normal round one on E. coli Bs/3 strain in nature, but the character is so unstable on E. coli B that it easily mutates back to T3hm⁺. If the mutation occurrs at an early stage during the development of T3 hm phage, the irregular plaque which has the protruded area where the phage mutated back is formed.
The existence of a minute mutant recognizable only on E. coli B in which mutation from m to m⁺ occurs so frequently and so easily that it forms an irregular plaque, is shown in this study but it has not yet been clarified whether the mutation occurs by the recombination between the bacteria and phage or only by a spontaneous mutation i.e., a mutable gene.

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When E. coli. B is mixed with T3 phage, the T3 phage-resistant colonies appear. Among these colonies, the chewed up sectored colonies are frequently observed. The colonies and lysing phages were maintained by transferring on the agar slant medium. After several transfers, the phage was isolated and designated as T3hs phage, because it was h mutant of T3 phage which produced the irregular plaques on E. coli B wild type strain (Okada, 1958).
The reason why the plaques of T3hs phage on E. coli B were so irregular was disclosed by Doi. The T3hs phage was T3hm phage which manifests its minute character only on E. coli B wild type strain and not on E. coli Bs/3 strain which prepared from the sectored colonies. During the development of T3hm phage on E. coli B, the mutation from m to m⁺ occured and the area of the development of back mutated T3hm⁺ was so protruded that the plaques became irregular (Doi, 1958).
Next problem is to determine whether the behavior of Bs/3 strain to T3hm phage is specific for Bs/3 strain or common for B/3 strains. To dissolve this question, several phage resistant bacteria (to T1-T7) were prepared and tested for the behavior to T3hs phage. Then, it was concluded that the mutations of E. coli B to T3, T4 resistance were always accompanied by the alteration of the behavior to T3hs phage.

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