Abstract
1) Drosophila montium is one of the tropical species distributed widely in the Eastern Hemisphere: Africa, Formosa, Java, India, Samoa, Sumatra and southern regions of Japan and China.2) Two races, A and B, may be distinguished in this species by the difference in chromosome complex, The oogonial metaphase plate includes four pairs of chromosomes, namely, two large V-shaped pairs, a rod-shaped pair (X's) and a pair of small chromosomes, which are V-shaped in Race A and rod-shaped in Race B. In the male, one of the rod-shaped X's is replaced by a small V-shaped Y. In the salivary gland nucleus, six strands radiate from the chromocenter. One of these is much shorter than others and is attached to the chromocenter with both ends like a ring. This apparently corresponds with the short rod and small V found in the metaphase complex.3) Thirty mutants have been discovered, of which twenty-five are assigned to three linkage groups. The mutants are described briefly.4) Percentages of spontaneous non-disjunctions and of those obtained by X-ray treatment are given.
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