66 LABORATORY DIRECTIONS 



expanded sac, the urogenital sinus, Into which the seminal 

 vesicle and ureter empty. Try to find the openings of these. 



The elasmobranchs are peculiar in that there are two meso- 

 nephric ducts. In most animals with mesonephric kidneys a 

 single duct serves for the passage of both urine and sperm. 



Urogenital Organs of the Female Shark 



The ovaries are elongated bodies on each side of the anterior 

 part of the body cavity. Each is held to the dorsal body wall 

 by a fold of the peritoneum, known as the mesovarium. The 

 lobulated character of the ovaries is due to sac-like /o//2V/<?j, each 

 of which contains an egg. The size of the ovaries depends upon 

 the state of development of these eggs. The ovaries are not 

 connected with any duct, but the eggs when ripe simply break 

 through the ovarian wall into the body cavity. 



On the inner surface of the ventral body wall, near the 

 anterior end of the liver, is a loose membrane with a longitudinal 

 slit. This slit is the ostium tubae, the common opening of the 

 two oviducts or Mullerian ducts. The oviducts pass dorsally, 

 one on either side of the liver, and then caudally. The posterior 

 swollen portion of each duct is the uterus. The ripe eggs that 

 have entered the body cavity from the ovary, pass through the 

 ostium tubae, enter the narrow part of the oviduct, and finally 

 reach the uterus. In viviparous sharks, like this species, the 

 young develop here. Between uterus and ostium there may be 

 found a small swelling, the shell gland. The Mullerian ducts 

 enter the cloaca close together and dorsal to the urinary papilla. 



The kidneys of the shark are known as Wolffian bodies or 

 mesonephroi. They consist of a pair of elongated structures 

 extending almost the whole length of the body cavity, dorsal 

 to the peritoneum and near the median line. The posterior 

 part of each is wider and thicker than the anterior, and appar- 

 ently is the only part that functions as an excretory organ in 

 adults. 



The ureter or accessory mesonephric duct runs along the 

 median edge of the posterior part of the kidney, somewhat 

 embedded in tissue. Beginning at the lateral edge of the kidney 

 remove the peritoneum to expose this duct. The ducts from 



