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Across: 1. Process by which a sperm's nucleus fuses with that of an egg forming a zygote. (13) 3. Sexual intercourse. (10) 9. Inner layer of uterus wall; site of implantation of embryo. (11) 11. One of many hair-like structures present in an oviduct that sweep the egg along towards the uterus. (6) 12. Female sex cell. (3) 13. Embryo at a later stage of development when its species can be determined from its appearance. (6) 16. Part of female reproductive system that produces eggs. (5) 18. Fertilised egg and first cell of a new individual. (6) 19. Male organ containing tube to testis; used to introduce sperm into female. (5) 20. Milk-producing organ of female mammal. (7,5)

Down: 2. Production of new members of a species. (12) 4. Part of male reproductive system that produces sperm. (6) 5. Period of development of a mammalian embryo inside the mother's body. (9) 6. Multicellular structure formed from a zygote by repeated cell division. (6) 7. Hollow muscular organ of female mammal within which the embryo develops. (6) 8. Liquid-filled sac that bathes and cushions the mammalian embryo. (6) 10. General term for a sex cell. (6) 14. Male sex cell. (5) 15. Disc-shaped organ that allows selective exchange of materials between the bloodstreams of the embryo and the mother. (8) 17. Tube possessed by female mammal that leads to the uterus; receives penis of male during copulation. (6)