This creature has a detachable arm called a hectocotylus that carries sperm. It actually breaks off and swims to the female independently [1]. Why the Variation?
Many mammals, including dogs, bears, and most primates (but not humans), have a physical penis bone called a baculum. This helps maintain stiffness without relying solely on blood flow [4].
The world of animal biology features an incredible variety of reproductive adaptations, often shaped by "sexual selection"—the evolutionary pressure to successfully pass on genes in challenging environments. The Diversity of Forms
Most birds (about 97%) actually lack an external phallus. Instead, they have a cloaca , and mating occurs through a brief "cloacal kiss." However, waterfowl like ducks are famous exceptions. They possess corkscrew-shaped organs that can reach lengths equal to their entire body, an evolutionary response to complex reproductive competition [1, 3].