Sperm cells. These are cells that semen carries that can fertilize an egg cell and make someone pregnant. Sperm cells look like microscopic tadpoles and they carry genes of the body that made them. The testicles make sperm. When semen ends up inside a vagina, sperm cells will try to swim into the womb and eventually the fallopian tubes, where an egg cell will be during the ovulation period of the womb owner’s reproductive cycle. In biology, sperm cells are also called spermatozoa, or male gametes.