GAMETOGENESIS, in embryology, the name given to an abnormal form of egg fertilisation due to the entrance of a number of spermatozoa into the ovum instead of one as in normal fertili sation. A corresponding number of male pronuclei are formed, and the subsequent development, if it takes place at all, is ab normal. The spermatozoa and ova are called the gametes. In the Arthropoda, selachians, amphibians and mammals the reproductive organs can admit of several spermatozoa normally entering the ovum, but of these only one forms a male pronucleus, the rest being absorbed. See EMBRYOLOGY, HEREDITY, SEX.