Examine the photographs of the dorsal wall of the body cavity of the male spiny dogfish shark by clicking the blue lettered links in the column to the right. The specimen in the phographs was prepared by removing almost the entire liver, alimentary canal, pancreas, and spleen. This revealed the urogenital structures: gonads, kidneys, and associated ducts.

The urinary and genital systems have distinct and unique functions. The first, the removal of nitrogenous wastes and the maintenance of water balance; the other, the reproduction of species. However, due to their similar developmental origins and the sharing of common structures, they are usually considered as a single system.

The shark kidney and its ducts are quite different from those in higher vertebrates. The relationship between the urinary and genital structures is also quite different.

The kidneys are flattened, ribbon-like, darkly colored structures Iying dorsally on either side of the midline, along the entire length of the body cavity. A tough white glistening strip of connective tissue is found between the kidneys in the midline.

The kidneys of the male are essentially the same as those of the female. The posterior portion is involved in the manufacture and transport of urine. The main difference lies in the anterior portion of the kidney, which in females is degenerate and functionless, but in males is an active part of the reproductive system.

Shark Kidneys

Labeled Kidneys

Examine the anterior view photographs of the shark by clicking the blue lettered links in the column to the right.

Paired testes lie near the anterior end of the body cavity, dorsal to the liver, adjacent to the anterior ends of the kidneys.The sperm pass from the testes to the kidneys within narrow tubules called efferent ductules.

Shark Testes

Labeled Testes

Examine the bottom view photographs of the shark by clicking the blue lettered links in the column to the right.

After passing through the anterior end of the kidney the sperm enter the ductus deferens and pass posteriorly toward the cloaca. In mature male specimens the ductus deferens may be seen on the ventral surface of the kidneys as a pair of highly coiled tubules.

Note: While in the female this duct carries urine, in the male it transports spermatozoa and seminal fluid.

The posterior portion of the ductus deferens widens and straightens to form the paired seminal vesicles.

Shark Ductus Deferens

Labeled Ductus Deferens

Examine the photographs of the shark's seminal vesicles by clicking the blue lettered links in the column to the right.

The paired sperm sacs at the posterior ends of the seminal vesicles receive the seminal secretions. They join to form the urogenital sinuses which exit through the fleshy conical urogenital papilla which extends from the cloaca.

The accessory urinary ducts, collect and transport urine from the kidneys. These paired thin tubules may be found along the medial side of the posterior half of the kidney. Small collecting tubules from the kidneys lead into the accessory urinary ducts along their lengths.

The cloaca receives the genital and urinary products as well as the rectal wastes.

Shark Seminal Vesicles

Labeled Seminal Vesicles

Examine the photographs of the shark's claspers by clicking the blue lettered links in the column to the right.

The claspers are modified extensions of the medial portions of the pelvic fins. They are inserted into the female's cloaca during copulation.

The finger-like claspers each have a dorsal groove, the clasper tube that carries the seminal fluid from the cloaca of the male to the cloaca of the female during mating.

Shark Clasper Tubes

Labeled Clasper Tubes

Examine the photographs of the dorsal wall of the body cavity of the female spiny dogfish shark by clicking the blue lettered links in the column to the right. The specimen in the phographs was prepared by removing almost the entire liver, alimentary canal, pancreas, and spleen. This revealed the urogenital structures: gonads, kidneys, and associated ducts.

The ovaries are two cream-colored elongated organs in the anterior part of the body cavity dorsal to the liver on either side of the mid-dorsal line. The shape of the ovaries will vary depending upon the maturity of the specimen. In immature females they will be undifferentiated and glandular in appearance. In mature specimens you may find two to three large eggs, about three centimeters in diameter, in each ovary. When these break the surface of the ovary, upon ovulation, they enter the body cavity and by means of peritoneal cilia are moved into the oviducts.

Shark Ovaries

Labeled Ovaries

Examine the photographs of the female shark's oviducts by clicking the blue lettered links in the column to the right.

The oviducts are elongated tube-like structures Iying dorsolaterally the length of the body cavity, along the sides of the kidneys. In mature specimens they are more prominent. The distal half of the oviduct is enlarged to form the uterus.

The shell gland is the anterior end of the oviduct. The eggs are fertilized and receive a light shell-like covering as they pass through the shell gland.

Shark Oviducts

Labeled Oviducts

 Examine the photographs of the female shark's uteri by clicking the blue lettered links in the column to the right.

The posterior half of the oviduct becomes enlarged and is known as the uterus. The fertilized eggs develop into embryos in the uterus. Upon completing their period of gestation (close to two years) the young are ready to be born.

The cloaca serves for the elimination of urinary and fecal wastes as well as an aperture through which the young "pups" are born.

The two uteri open into the posterodorsal portion of the cloaca just ventral to the urinary papilla.

Fertilization in the dogfish shark is internal, usually taking place within the shell gland of the oviduct. The fertilized eggs continue to move posteriorly to the uterus. As they grow the pups are attached to the egg, now known as the yolk sac, by means of a stalk. During its period of gestation, which is nearly two years, the yolk is slowly absorbed by the shark "pup."Numerous uterine villi, finger-like projections from the uterine wall, make contact with the surface ot the developing embryo and its yolk sac. It is believed that these provide the embryo with water; all other nutrients are supplied by the yolk. At birth the young are about 23 to 29 centimeters long. This type of development, where the young are born as miniature adults but have received hardly any nutrition directly from the mother's uterus, is known as ovoviviparous.

Shark Uteri

Labeled Uteri