Unlike many mammals, lizards do not possess external scrotal sacs or “balls” in the mammalian sense. Male lizards are equipped with distinct internal reproductive organs that allow for successful reproduction. Their anatomy differs significantly from what is commonly observed in mammals, reflecting adaptations to their environment.
Understanding Lizard Anatomy
Their gonads are located internally, typically within the abdominal cavity near the kidneys. These internal testicles produce sperm and testosterone, increasing in size during the breeding season. This internal placement is a common characteristic among reptiles, offering protection and supporting temperature regulation for sperm production.
Lizards possess a single, multi-purpose opening called the cloaca, which serves as a common exit point for their digestive, urinary, and reproductive systems. This chamber is divided into three sections: the coprodeum for feces, the urodeum for urine and reproductive products, and the proctodeum, which is the final section before the external vent. Within the cloacal region, male lizards house their unique paired reproductive organs, known as hemipenes. These two structures are typically held inverted and tucked away inside the base of the tail when not in use.
The Role of Hemipenes in Reproduction
Hemipenes are the functional equivalent of a mammalian penis, though structurally distinct as they are paired and internal. During copulation, one of the two hemipenes is everted from the cloaca through the action of erectile tissue and muscles. Although male lizards have two hemipenes, only one is typically used at a time for sperm transfer during a single mating event.
Sperm travels along a specialized groove, called the sulcus spermaticus, located on the outer surface of the everted hemipenis. This allows for the direct transfer of sperm into the female’s cloaca. Fertilization in lizards is internal. Many species of lizards have hemipenes with various ornamentations like spines, hooks, or knobs, which are thought to help secure the male during the mating process.
Distinguishing Male and Female Lizards
Identifying the sex of a lizard can be challenging. However, several secondary sexual characteristics can help differentiate males from females. Males of many species often exhibit more vibrant coloration, which they use to attract mates and display dominance.
Size and head shape can also be indicators, with males frequently having larger heads and sometimes a larger overall body size compared to females. Many male lizards, particularly those in the Iguanidae family, possess prominent femoral pores on the underside of their hind legs or pre-anal pores, which secrete waxy pheromones for chemical communication and territorial marking. While females may have these pores, they are typically smaller or absent. Another visual cue in males can be slight bulges at the base of the tail, caused by the presence of the inverted hemipenes.