DO SPERMATOZOA PENETRATE THE MEMBRANE OF SELF-INSEMINATED EGGS OF CIONA AND STYELA?

¹ William G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadenaa

A comparison of unfertilized eggs of Ciona with self- and cross-fertilized eggs show that spermatozoa do not, as a rule, penetrate the membrane of their own eggs. Rarely a sperm may be found inside a self-inseminated egg, which is consistent with the fact that occasionally self-fertilization occurs. Even in cross-fertilized eggs only a very few sperm are found inside the membrane of such eggs. The same statement holds for two species of Styela examined, except that a few more sperm are likely to be found inside the membrane of the self-inseminated eggs, which is consistent with the fact that self-fertilization is more frequent in these species than in Ciona.