MALE MEIOSIS IN POLYPLOID SILKWORMS, BOMBYX-MORI L (LEPIDOPTERA, BOMBYCIDAE)

Tetraploid and hexaploid silkworms, Bombyx mori L. (Lepidoptera : Bomb ycidae) were induced by applying a cold shock to diploid and triploid eggs at the first cleavage stage. Male meiosis in the primary spermato cytes of these silkworms having a different ploidy was observed. In th e polyploid cells, chromosome bridges, 2 for the tetraploid and 3 for the hexaploid, occurred between the newly formed daughter nuclei at te lophase. Observation in the living spermatocytes showed that tetraploi d cells needed a longer time than the diploid ones to complete the fir st meiotic division. The delay in the cell division may be responsible for the high sterility of the tetraploid males.