Abstract
The ganglia of old larvae of Drosophila virilis reared under favourable conditions contain many somatic cells in the process of mitotic division. Through the treatment of the larvae under unfavourable culture conditions, the process of the mitotic division in ganglion cells is suppressed, and as a consequence most of these cells remain in the resting stage for longer time than in the normal mitosis. This condition leads to the production of bivalent chromosomes in some ganglion cells, which were produced due to the synaptic pairing of homologous chromosomes, being six in number (n), instead of 12, the 2n number. The prolongation of the resting stage would permit in the nucleus the homologous chromosomes to become intimately associated in pairs. The evidence presented implies that mitosis becomes convertible by a retardation of the division process into meiosis.
