Selection for the outward phenotype after cold-shock treatment steadily increased the proportion of the outward individuals up to the fifth generation (Fig. (Fig.4A).4A). In the fifth generation, the outward type occupied 80% of the total population. The outward sensitivity to the treatment was increased fairly quickly despite the fact that selected individuals were crossed with field-caught individuals every generation. The proportion of the normal individuals decreased gradually to the tenth generation, indicating the feasibility of the selective breeding procedure. Most tenth generation cold-shocked individuals showed extensive outward modifications (Fig. 4E-G). Throughout the generations, the outward type comprised more females than males, as in the Fukaura case (Fig. (Fig.4B).4B). Inversely, the reduction type comprised more males than females, also similar to the Fukaura case.