Abstract
Drosophila nigromaculata is known as a species showing remarkable chromosomal polymorphism in natural population. Toyofuku (1960, 1962) reported the standard map of salivary chromosomes and 22 different inversions in this species obtained from some localities of Hokkaido. Further observations were undertaken by the present author during a period from late June to October, 1962, in the University Botanical Garden, Sapporo. The author found 33 different inversions in heterozygous condition based on the examination of 569 larvae derived from 47 females. The number of inversion types in each chromosome was as follows: 5 different inversions in X chromosome, 10 in A chromosome, 7 in B chromosome, 8 in C chromosome and 3 in D chromosome. Out of 33 inversions found by the author, 14 were not reported by Toyofuku. Their distribution on chromosomes is as follows: 3 in X chromosome, 3 in A chromosome, 4 in B chromosome, 3 in C chromosome and 1 in D chromosome. Frequency of each inversion in natural population seems to be variable by season.
