The homologies of the various copulatory organs in reptiles have been widely debated. Available data suggest that the embryological development of the hemipenes in lizards and snakes is less complex than the development of the sex organ in turtles. The embryological development of the copulatory organ in crocodilians is yet to be studied comprehensively.

Male and female crocodiles have a homologous structure generally similar in gross morphology. This is called a cliteropenis by some researchers. Others use the term penis or phallus for this structure in males. Although there may be a lack homology between squamate hemipenes and the chelonian (turtle) or crocodilian penis, research indicates that the steroid environment during embryonic development directly influences the development of the sex organ. In some species of reptiles, phallic development is stimulated by the presence of androgens, as observed with placental mammals. In other species of reptiles, phallic development is inhibited by estrogens, as in birds.