The major principle of behaviorism was that psychology should study covert responses. Darwin and others believed that animals and humans had similar behaviors, whether or not either or both had minds.
Structuralism is like physiology, and functionalism is like anatomy.
One of the leading functionalists was Wundt. It is perhaps not surprising that functionalism and subsequently behaviorism had its roots in the corn belt of America, Columbia University. Dewey's reflex arC referred to the fact that there is no simple division between a stimulus and a response. The law of exercise stated that the more practice the stronger was the habit. The law of effect said that the effect of practice was increased learning.