Which theory proposed by William Harvey states that all parts of the embryo are present potentially in the egg?

• A. Preformation
• B. Epigenesis
• C. Cell theory
• D. Germ plasm theory

Answer: (B)

The correct theory proposed by William Harvey is preformation. This idea posits that all the structures of the adult organism are pre-formed within the egg or sperm and that development is merely the growth and unfolding of these structures over time. Preformation suggests that the organism exists in a miniature form within the gametes before actual development begins.

Harvey's work laid the groundwork for understanding embryo development, but it's important to note that he himself did not assert that all parts of the embryo are present in their complete form within the ovum. Instead, preformation was a more commonly held belief during Harvey’s time, which posited that the entire organism was pre-formed and simply grew larger during development. In contrast, epigenesis (another idea debated around this time) proposed that the embryo develops progressively and that structures arise from nothing, which is contrary to the preformation concept.

Overall, preformation encapsulates the core idea that the embryo’s eventual parts are all intrinsically present at the start, reflecting the nature of embryonic development as conceived by Harvey and his contemporaries.