The answer to whether lizards have two penises is yes, many do. This paired structure is a defining feature of the males in a massive group of reptiles, including all lizards and snakes. Scientists refer to these twin reproductive organs as hemipenes, a term that immediately distinguishes them from the single copulatory organ found in mammals and other reptiles. These structures are inverted and stored within the tail base, only becoming apparent when everted for mating.
Confirmation of the Dual Structure
The term “hemipenes” literally means “half penises,” referring to the two mirror-image structures tucked into a pocket in the tail just behind the cloaca. When not in use, these organs are entirely internal and inverted, resembling a pair of small, tucked-in sacs. This differs fundamentally from the single, unpaired phallus present in most other amniotes, such as turtles, crocodiles, and mammals. Unlike the mammalian penis, which arises from embryonic cells that develop the tail, hemipenes originate from the same embryonic cells that form the hind limbs.
These paired organs function exclusively for sperm transfer and are not part of the urinary tract, which uses the cloaca for waste elimination. The singular nature of the mammalian penis, which contains a urethra for both urination and reproduction, contrasts sharply with the specialized, separate role of the hemipenes. The internal storage of the hemipenes often results in males having a visibly wider or thicker tail base compared to females.
The Unique Anatomy of Hemipenes
The structure of the hemipenes is highly specialized and varies dramatically across different species of lizards and snakes. Each hemipenis is essentially a pouch of eversible tissue that turns inside out upon deployment. A defining anatomical feature is the sulcus spermaticus, which is a groove or channel running along the outside of the organ rather than an internal tube. Sperm travels down this open channel during copulation, relying on the contact with the female’s cloacal wall to form a temporary closed path.
The surface of the hemipenes is often covered in elaborate ornamentation, which can include spines, hooks, papillae, or calyces (cup-like structures). This extensive surface texture is thought to be a mechanism for anchoring the male securely within the female’s cloaca during copulation. The diverse shapes and surface features of these organs are so specific that they often act as a reproductive “lock-and-key” mechanism, ensuring that only males and females of the same species can successfully mate. Although two organs exist, only one is typically everted and used to inseminate the female during a single mating event.
Mechanics of Reproductive Use
The eversion of a hemipenis, the process of turning it outward from the tail base, is not accomplished by muscle contraction like many mammalian erections. Instead, the process is primarily driven by hydrodynamic pressure. Lymphatic fluid or blood fills the vascular spaces within the organ, causing it to rapidly engorge and push itself outward through the cloacal opening. This fluid-driven mechanism provides the necessary rigidity and force for intromission.
Following copulation and the transfer of sperm, a specialized set of retractor muscles is responsible for pulling the inverted organ back into its storage pocket in the tail. The evolutionary advantage of possessing two separate organs is twofold, addressing both physical positioning and reproductive efficiency. Having a left and a right hemipenis allows the male to use the organ best positioned to align with the female’s cloaca, providing flexibility regardless of their mating posture.
Furthermore, the dual system allows for the possibility of rapid consecutive matings. Since each hemipenis is associated with the testis on the same side, using them alternately may allow one organ to recover or “recharge” its sperm supply while the other is in use.
Which Reptiles Share This Trait
The presence of hemipenes is a defining characteristic of the entire taxonomic order Squamata, which encompasses all lizards, snakes, and the less-known amphisbaenians (worm lizards). Squamata is the largest order of reptiles, containing over 9,000 species worldwide.
The hemipenes distinguish these reptiles from all other major groups within the class Reptilia. For example, male members of the Testudines (turtles and tortoises) and the Crocodilia (crocodiles and alligators) possess a single, median phallus. These other reptiles have a single copulatory organ. Therefore, the dual-organ system is restricted to the snakes and lizards, highlighting a distinct evolutionary path for their reproductive biology.