70 VERTEBRATE ZOOLOGY 



The Male Genital Organs. The testes are a pair of yellowish, 

 cylindrical bodies, each of which is attached to the dorsal body 

 wall by a mesentery. Delicate tubes, the vasa efferentia, connect 

 the testis with the median border of the kidney on each side. Hold 

 the mesentery to the light and note these vessels, which are sus- 

 pended in it. Spermatozoa are produced in the testes and pass 

 through the vasa efferentia into the kidneys, whence they find their 

 way into the Wolffian ducts. These organs thus perform the 

 double function of conducting to the outside both the urine and 

 the spermatozoa; on this account they have received a special 

 name and are called also ducts of Leydig. It is only in elasmo- 

 branchs and amphibians that Leydig's duct is present. 



The Female Genital Organs. The ovaries are a pair of irregular, 

 elongated bodies which lie in the body cavity, attached to its 

 dorsal wall by mesenteries. They vary in size with the sexual 

 condition of the animal. The ova are emitted into the body cavity 

 by the rupture of the wall of the ovaries, whence they pass to 

 the outside through the oviducts, or Mullerian ducts. These are a 

 pair of thick-walled, convoluted tubes which extend from the for- 

 ward end of the abdominal cavity to the dorsal wall of the cloaca. 

 Note carefully the funnel-shaped ostium, the anterior end of the 

 oviduct which opens into the body cavity. Separate the margins 

 of the ostium and observe the opening. The hinder end of each 

 oviduct is not convoluted and forms the uterus, a receptacle in 

 which the ova are stored at the time of laying. 



Observe carefully these organs and note their exact position. 

 Slit open the cloaca and find the mouths of the ureters and of 

 the oviducts (if the animal is a female). 



Exercise 7. Draw a semidiagrammatic sketch of the urogenital sys- 

 tem, showing accurately the position of the urogenital organs. 



The Respiratory System. The principal organs of respiration 

 are the outer skin and the gills. The lungs, which also aid in res- 

 piration, are a pair of very long cylindrical sacs extending back 

 in the abdominal cavity from the ventral wall of the pharynx. 

 Note that the two lungs meet immediately before they open into 

 the pharynx through the glottis; a windpipe or trachea is thus 



