Fertilization and the first cleavage mitosis in insects.

Fertilization in animals is now considered to be of the "sea urchin type"; that is, haploid male and female pronuclei completely fuse shortly after sperm entry into the egg, followed by the formation of a mitotic spindle to allow cleavage mitoses to proceed. However, two other patterns of fertilization and early embryonic mitosis in some animal species are known: an Ascaris type and a gonomeric type. The gonomeric type of fertilization in insects and other arthropods is not well known and is quite different from the sea urchin and Ascaris types. In the present article, the author examines the peculiar gonomeric fertilization, using mainly the silkworm as an example.