A pair or pairs of heteromorphic chromosomes are of special importance for cytogenetic analysis, for reductional and equational separations for the inequality are distinguished at AT. Based on the chiasmatype hypothesis, frequencies of these two types of AT separation are governed by crossing-over in the region of the chromosomes concerned (cf. Mather 1935, Darlington 1937. Observations of frequencies of chiasmata and the types of AI separation in heteromorphic chromosome pairs of various sources have shown close relationship between crossing-over and chiasma formation, supporting the view of the chiasmatype hypothesis (Brown and Zohary 1955, Jamn and Basak 1963, Kayano 1960a, b, Kayano and Nakamura 1960, Noda 1960, 1967, Zen 1961).Nur's (1961) data also support the above view. The present state of the problem has been reviewed by Brown and Zohary (l. c.) and by Whitehouse (1965). The purpose of the present paper is to show additional evidence of a close relationship between crossing-over and chiasma formation, and also to show no reduction of number of chiasmata from diplotene to MI, use being made of structural heterozygotes of Acrida lata Motschulsky (Orthoptera, Acrididae).
MATERIALS AND METHODSThree males of Acrida lata Motschulsky were used : (1) A translocation heterozygote, 2n-22 I X, caught at Goshi, Kumamoto Prefecture in 1963, (2) an individual, 2n=22 } X 1B, with a heteromorphic bivalent in primary spermatocytes, which was caught on the campus of Ooita University in 1962, and (3) a heterozygote for a centric fusion, 2n=21 H -X, caught on the campus of Kumamoto University in 1961. The testes were fixed in the mixture recommended by Newcomer (1953) and the preparations of spermatocytes were made employing the usual iron-acetocarmine squash method.
RESULTS AND DISCUSSIONCrossing-over and chiasma formation. In the translocation heterozygote the complex of 4 chromosomes was found to pair in 1 (6.5 °o), 1 --1 (91.7 %), 2 a (0.9 %), and 1 A } 2 1 (0.9 %), 217 primary spermatocytes at MI being observed (Fig. 2). Analysis of the configurations of the multiples indicated that a segmental interchange occurred between chromosomes 3 and 9, giving rise to chromosome 39 and 93 (Figs. 1, 2, and 6). The 1) Contributions from the Institute of Biology, Ooita University, No. 72.