22 THE SKATE 



toneal cavity. Each ovary is attached to the structures 

 dorsal to it by a mesentery, the mesovarium. Dorsal to the 

 ovary is the oviduct, an enlarged tube which is connected 

 with it only by mesentery. Dissect away this mesentery. 

 Trace one of the oviducts forward and notice in your speci- 

 men or in a demonstration specimen that its narrow an- 

 terior portion passes along the dorsal coelomic wall, curves 

 around the anterior dorsal margin of the liver and unites 

 with its fellow from the other side, where is located the 

 ostium, a wide funnel-shaped opening for receiving the 

 eggs after they break out from the ovary into the coelom. 

 Trace the oviduct caudad and notice an enlargement of 

 the tube, the uterus. At its beginning is a bilobed mass, the 

 oviducal gland, which secretes the horny case (see demon- 

 stration) in which the eggs are contained. Egg cases will 

 often be found in the uterus of the skates being dissected. 



Drawing 11. Draw the female urogenital system. 



B. The Male. 



The testes in which the sperm cells are developed are 

 oval flat bodies (about 60 mm. x 20 mm.) attached to the 

 more dorsal structures by mesenteries, the mesorchia. The 

 kidney or excretory organ is like that of the female. Dis- 

 sect it out after the manner outlined above for the female. 

 The mesonephric or "Wolffian ducts are well developed tubes 

 running posteriorly along the ventral faces of the cranial 

 mesonephros. They serve as a passageway for the sperm 

 cells. They are greatly convoluted tubes located near the 

 median line. 



The testis is connected with the cranial mesonephros by 

 means of delicate ducts, the vasa efferentia, which run in 

 the mesorchium. These vasa efferentia connect with tubules 

 of the mesonephros. The sperm tubules of the mesonephros 

 connect with the Wolffian duct. Trace the duct and notice 



