Abstract
1. The diploid complement in the males of Anisops niveus, A. fiebri and A. sardea is represented by 26 chromosomes while in the females, studied only in A. niveus, it consists of 28 elements. 2. The sex determining mechanism is of the X1X20-male and X1X1X2X2-female type in all the three species. The sex chromosomes divide reductionally in the first meiotic division of the male. 3. A pair of m-chromosomes is present in each species while a pair of supernumerary elements occurred in some individuals of A. niveus. 4. The X1X20-male sex mechanism has probably originated from a simple XY type, similar the one still existing in Notonecta indica, by the loss of Y and conversion of the simple X into a multiple one, accompanied by a change in their division sequence. 5. The change from the typical heteropteran post-reductional sex chromosome behaviour to the pre-reductional one, is suggested to be the result of the delay in their kinetochore interaction with the division centres during the first meiotic division, in all the three species of the Anisopinae.
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