The excretory and reproductive systems are so closely related to each other in vertebrates that they are considered together under the name of the “urinogenital system”.
Male Urinogenital System

Fig: Male urinogenital system of Scoliodon
A. Male Excretory System
- A pair of kidneys are the main excretory organs of the male Scoliodon.
- The kidneys are mesonephric type.
- They are long, flattened, and ribbon-like.
- They are attached to the dorsal abdominal wall, above the peritoneum, one on either side of the median line.
- They extend nearly the whole length of the body cavity from the root of the liver in front up to the cloaca behind.
- The anterior part of the kidneys is non-excretory and they are genital in function. Hence they are called the epididymis.
- The posterior part is greatly developed and it is the main excretory part. The posterior part forms the functional adult kidney, called opisthonephros.
- Each kidney is formed by uriniferous tubules, Bowman’s capsule, and glomeruli.
- The tubules have a special urea-absorbing segment in them.
- Posteriorly, both the ureters open into a urinogenital sinus.
- The urinogenital sinus opens into the cloaca.
B. Male Reproductive System
- A pair of very large and elongated testes are the principal reproductive organs of male Scoliodon.
- They are attached to the mid-dorsal abdominal body wall by a double fold of peritoneum called mesorchium.
- From each testis, several very fine tubules are given off, called the vasa efferentia.
- The vasa efferentia run in the mesorchium to the anterior end of a large Wolffian or mesonephric duct now called the vas deferens.
- Spermatozoa developed from germ cells in seminiferous tubules of the testis by the process called spermatogenesis.
- The vas deferens forms a very large and extremely coiled duct that produces fluid for the nourishment of the spermatozoa.
- Posteriorly the vas deferens expands to form the seminal vesicle which is a wide straight tube.
- The seminal vesicles of both the sides open behind independently into the urinogenital sinus.
- The urinogenital sinus later opens into the cloaca.
- Claspers and siphon are the accessory parts of the male reproductive system.
- Claspers are present on the pelvic fins of male dogfish.
- Siphon is a muscular sac beneath skin of posterior ventral pelvic region.
- During copulation, sea water is drawn into siphon and forced down the clasper groove flushing spermatozoa accumulated there into the female cloaca.
Female Urinogenital System

Fig: Female urinogenital system of Scoliodon
A. Female Excretory System
- Two kidneys are the main excretory organs.
- The kidneys are mesonephric type.
- The anterior portions of the kidneys are non-excretory.
- The posterior portions of the kidneys are the main excretory parts.
- In the female urinogenital system, there is no connection between the kidneys and genital organs.
- Therefore, the anterior part of the kidney is extremely reduced.
- The uriniferous tubules of the posterior functional part of the kidney open into a long thin-walled duct, the ureter.
- Unlike male, the two ureters of female dogfish unite into a common median ureter opening behind into the large median urinary sinus.
- The sinus later opens into the cloaca.
B. Female Reproductive System
- Female genital organs are one pair of small ovaries.
- They are attached one on either side mid-dorsally to the anterior abdominal wall by a fold of peritoneum, the mesovarium.
- Their form and size vary with the age.
- A pair of long tubular epigonal organs extend between ovaries.
- Mature ova are shed into the abdominal cavity from where they enter the oviducts.
- The two oviducts or Mullerian ducts are large tubes, extending the whole length of the body cavity.
- The two oviducts remain united both posteriorly and anteriorly.
- Anteriorly two oviducts unite mid-ventrally, below oesophagus to open into coelom by a single longitudinal slit, the ostium or oviducal funnel.
- Each oviduct bears a shell gland that secretes a thin membrane over the descending eggs.
- Posteriorly, two oviducts unite to form the vagina which opens into the cloaca.
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Read More :
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