Abstract
The regional variations of number of the anal fin-rays were examined of 4437 wild specimens of Oryzias latipes collected at 56 different localitis in Japan. The results obtained are given in table 1, as “ frequency distribution curve, ”in fig. 1. Fig. 2 is a map showing the mean value of the fin ray counts of the fish caught at the respective locality. From the results, the following may be concluded:
(1) Within the neighbouring localities belonging to the same watershed, the averages of the number of the rays do not show a significant difference.
(2) The differences are often significant among the fish living in the waters situated at the isolated regions.
(3) The number of the rays does not show a decrease or an increase according to the differences of the circumstances (temperature, for instance) at the locality.
(4) The geographical variation is caused not by the agents of environment, but chiefly by the differences of the gene-constitutions.
