INSEMINATION. INSEMINATION At fertilization, several thousand spermatozoids surround the ovum, but only one will enter the ovum and fertilize it. The spermatozoid penetrates the ovum by secreting enzymes which open the cell layers enveloping the ovum. Once the spermatozoid has entered the ovum, the genetic material contained in the nucleus of the ovum and the spermatozoid fusion. The tail of the spermatozoid falls off and the fertilized egg becomes impermeable to other spermatozoids.