Moreover, I learned that (fertilization, reproduction) could happen internally
or externally among animals. The union of an egg cell and a sperm cell that takes
place either inside a female body or inside an egg laid by the female is called (internal,
external) fertilization, and (internal, external) fertilization occurs when both sex cells
are out into the water or air. Animals have sex organs that produce sex cells, also
known as (embryo, gametes). The sex organ of the female is called (ovary, testis), and
for males, they are the pair of (ovaries, testes).​