Final answer:
William Harvey and Hans Speeman made important observations about embryonic development, highlighting the role of the environment and cell interactions.
Step-by-step explanation:
William Harvey's experiments in the 17th century led to the conclusion that the physical and chemical environment of an embryo affects its development. Hans Speeman's experiments in 1924 showed that cells associated with differentiation could induce new tissue development when transplanted. These findings highlight the importance of the environment and cell interactions in embryonic development.