A look at the embryonic underpinning of hemipenes and penises of other animals suggests that there are fundamental differences in their developmental stages, particularly their origin of development relative to the embryonic cloaca. This theory proposes that the single unpaired penis is the ancestral state for amniotes, and that this trait was retained by most amniotes today. However, embryonic and molecular research is beginning to shed light on the origin of the hemipenis. Much debate continues regarding the evolutionary origin of hemipenes and their relationship to the intromittent organs of other species. Squamate hemipenes also develop from a different cell origin, originating from the same embryonic cells that produce the limbs, whereas mammalian penises arise from the embryonic cells that develop the tail. They differ from the intromittent organs of most other amniotes such as mammals, archosaurs and turtles that have a single genital tubercle, as squamates have the paired genitalia remaining separate. The hemipenis is the intromittent organ of squamata, which is the second largest order of vertebrates with over 9000 species distributed around the world. The female homologue is the hemiclitoris. They come in a variety of shapes, depending on species, with ornamentation, such as spines or hooks. Hemipenes are usually held inverted within the body, and are everted for reproduction via erectile tissue, much like that in the human penis. Common House Geckos, mating, ventral view with hemipenis inserted in the cloacaĪ hemipenis ( PL: hemipenes) is one of a pair of intromittent organs of male squamates ( snakes, lizards and worm lizards). Male sex organ in squamate reptiles An everted hemipenis of a North American rattlesnake ( Crotalus adamanteus).

Male green anaconda size