Experiments on blocking and unblocking of first meiotic metaphase in eggs of the parthenogenetic stick insect Carausius morosus Br. (Phasmida, Insecta).

The eggs of the parthenogenetic stick insect Carausius morosus, which remain arrested in first meiotic metaphase until oviposition, must be activated in order to develop. The activating agent is oxygen from the air, which enters the egg cell through the micropyle. An exposure shorter than one minute is sufficient to release the blockage. In non-activated (micropyle-less) eggs the first metaphase chromsomes either degenerate or change into an interphase nucleus. This nucleus polyploidizes by endoreduplication, and then either degenerates or multiplies by amitosis. Similarly more generations of nuclei may arise resulting in a chaotic development. These nuclei survive better in the anterior region of the egg. The question of whether the cytoplasmic factors which control nuclear behaviour, also operate in eggs of C. morosus is discussed.