1. Sexual reproduction: it is an advanced form of reproductive mode. Due to the realization of gene recombination, organisms are constantly evolving, which is the most common way of reproduction.
Second, asexual reproduction: it can be divided into the following categories:
1. Parthenogenesis: It exists in arthropods, some reptiles and fish, and refers to the reproductive mode in which eggs develop into individuals without fertilization. There are occasional parthenogenesis (most of them belong to this kind), frequent parthenogenesis (Hymenoptera insects) and periodic parthenogenesis (aphids).
2. vegetative reproduction: refers to the reproductive mode that produces the next generation without forming germ cells (such as starfish and leeches). )
Some special reproductive methods:
1. Metamorphosis: After the males of some animals die in the group, the strong females will change their sex and become males to continue to maintain the reproduction of the group, such as some fish.
2. hermaphroditism: Most animals in Gastropoda are hermaphroditic, but they can't fertilize their eggs with their own sperm cells to reproduce. Two individuals must mate, fertilize each other or independently, and then produce the next generation.
Individual artificial, hermaphroditic and allogeneic fertilization is not the highest reproductive form of animals, but it is indeed the best reproductive mode.