Question

Earthworms are hermaphrodite and reproduce primarily by
A. Self-fertilization
B. Cross-fertilization
C. Asexually
D. All of the above

Answer 1

An earthworm is an invertebrate which belongs to the order Opisthopora. In reproductive biology, a hermaphrodite is an organism that produces gametes usually associated with both the male and female sexes possessing full or partial reproductive organs.

Complete answer: The fertilization of an ovum from one person with another's spermatozoa is allogamy or cross-fertilization. Autogamy, by contrast, is the term used for self-fertilization. In humans, an instance of allogamy is the fertilization event. In hermaphroditic species, self-fertilization occurs when the two gametes fuse in fertilization come from the same entity. In plants and certain protozoa, cross-fertilization is common. Earthworms are hermaphrodites, but due to their relative male and female genital aperture location, they do not fertilize their own eggs and are protandrous (that is, male sex mature earlier than female gametes). So, instead of self-fertilization, cross-fertilization takes place. Male and female gametes (sex cells) are fused from various individuals of the same species. In dioecious plants (those with male and female organs on different individuals) and in all animal species in which separate male and female individuals exist, cross-fertilization must occur. Many species have well-developed mechanisms that ensure cross-fertilization, even among hermaphrodites, i.e., those organisms in which the same individual produces both sperm and eggs. In addition, many of the hermaphroditic species that are capable of self-fertilization and also have cross-fertilization capabilities.
So, option B is the correct option.

Note: In animals, methods of cross-fertilization are similarly diverse. The males and females each shed their sex cells into the water and external fertilization occurs among most species that breed in aquatic environments. There is also internal fertilization between certain fishes and other aquatic breeders.