The male reproductive systems of birds, rabbits, and reptiles exhibit both similarities and distinct features, reflecting their unique evolutionary adaptations. This comparison focuses on the reproductive anatomy of three species: the garden lizard (Calotes), pigeon (Columba), and rabbit (Oryctolagus).
Male Reproductive System of Calotes (Garden Lizard)
In Calotes, the testes are small, white, ovoid structures located within the abdominal cavity, positioned anterior to the kidneys. Unlike mammals, there is no inguinal canal, and the spermatic cord is absent. The right testis typically lies slightly ahead of the left, attached to the dorsal body wall via the mesorchium, a double fold of peritoneum. From each testis, a coiled epididymis arises, although caput and cauda epididymis are not distinctly present. This epididymis extends into the vas deferens, which travels along the ventral surface of the kidney, merging with the ureter to form the urino-genital sinus. This sinus opens into the cloaca, and seminal vesicles are notably absent in Calotes. The reproductive system of male Calotes also includes hemipenes, paired copulatory organs situated under the skin behind the cloacal aperture. There are no specific glands associated with the genital system in this species.
Male Reproductive System of Columba (Pigeon)
In pigeons, the reproductive system shares certain characteristics with reptiles, such as the presence of white ovoid testes in the abdominal cavity below the anterior parts of the kidneys. The left testis is typically larger than the right, and as in Calotes, the inguinal canal and spermatic cord are absent. The mesorchium attaches each testis to the kidney, but unlike Calotes, epididymis is absent in pigeons. The vas deferens arises from the inner border of the kidney and runs parallel to the ureter, with both opening separately into the cloaca. Interestingly, the posterior end of the vas deferens expands to form a seminal vesicle, which plays a role in sperm storage. Pigeons lack copulatory organs, distinguishing them from reptiles and mammals.
Male Reproductive System of Oryctolagus (Rabbit)
The male reproductive system of rabbits reflects their mammalian physiology. The testes in rabbits are pink, ovoid structures located in scrotal sacs, which are external to the abdominal cavity. Unlike birds and reptiles, these sacs are connected to the perivisceral cavity via inguinal canals, and the spermatic cord extends from each testis to just behind the kidneys. The epididymis, present in rabbits, includes both the caput and cauda, which are extensions around the testis. The vas deferens travels through the inguinal canal, loops around the ureter, and opens into the uterus masculinus within the urinary bladder. In contrast to reptiles and birds, rabbits possess multiple glands associated with the reproductive system, including the prostate, Cowper’s, and perineal glands. Additionally, the male rabbit’s copulatory organ is a penis, composed of erectile tissue and covered by the prepuce.
Reproductive System of Male Calotes (Garden Lizard) | Reproductive System of Male Columba (Pigeon) | Reproductive System of Male Oryctolagus (Rabbit) |
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Testes are white ovoid bodies. | Testis white ovoid bodies. | Testes are pink, ovoid bodies. |
Testes lie in the abdominal cavity much ahead of kidneys. Inguinal canal is absent. | Testes lie in the abdominal cavity under the anterior parts of kidneys. Inguinal canal is absent. | Testes are extra abdominal and lie in the scrotal sacs which are the folds of the skin. They are connected with perivisceral cavity by inguinal canals. |
Right testis is a little ahead of the left one. | Left testis is a little bigger than the right one. | Right and left testes are symmetrical. |
Spermatic cord is not formed. | Same as in calotes. | A spermatic cord extends from each testis to a little behind the kidney of its side. |
Each testis is attached to the dorsal body wall by a double fold of peritoneum the mesorchium. | Each testis is attached to the kidney of its side by mesorchium. | Each testis is attached to the wall of scrotal sac by a short, thick, elastic cord 'gubernaculum'. |
From the inner end of each testis arises a much convoluted tube-epididymis. | Epididymis is absent. | Epididymis is present. |
Caput and cauda epididymis are not found | Same as in calotes. | Caput epididymis and cauda epi-didymes are the extensions of epididymis infront and behind the testis |
Epididymis is continued behind as long, narrow, coiled and delicate vas deferens. It passes backwards along the ventral surface of the kidney of its side and joins with the ureter to form urino-genital sinus which opens into the cloaca. | The vas deferens arises directly from the inner border of the kidney in the form of a narrow convolutec tube. It runs backwards outside the ureter parallel to it and both open dorsally by separate aperture in urodaeum of the cloaca. | The vas deferens passes through the inguinal canal and runs forward and enters into the abdominal cavity. So that a loop around the ureter of its side to open into sac-uterus masculinus which is present in the dorsal wall of the urinary bladder. |
Seminal vesicles are absent. | Posterior end of each vas deferens enlarges to form seminal vesicle. | Seminal vesicles are absent. |
There are no special glands associated with male genital system. | Same as in calotes. | There are prostate, couper's and perineal glands are associated with the male genital system. |
In male a pair of eversible copulatory organs hemipenes lie under the skin behind cloacai aperture | Copulatory organs are absent. | The copulatory organ in male is in the form of a thick muscular Penis. It is covered by skin loose fold prepuce or foreskin penis is made up of a spongy tissue containing blood vessels and it is erectile. |
Comparative Insights
The reproductive systems of birds, reptiles, and rabbits demonstrate clear adaptations based on evolutionary lineage. In reptiles, such as the garden lizard, internal testes, and the presence of hemipenes provide reproductive advantages in their environments. Pigeons, as birds, exhibit a simpler system with internal testes and an absence of copulatory organs, consistent with the avian adaptation of reducing body mass for flight. Rabbits, as mammals, exhibit a more complex system with external testes and specialized glands supporting reproduction. Each system is uniquely designed to meet the reproductive needs of these distinct species.