THE FROG 25 



(see below). They vary greatly in size in different speci- 

 mens. 



7. The reproductive system. This consists of the 

 gonads which produce the sex cells, and the ducts by which 

 the sex cells are carried to the outside. In order to make 

 a study of both male and female reproductive systems, sup- 

 plement the study of your own frog by the examination of 

 demonstration specimens. 



In the male observe the testis (male gonad), an oval pale 

 yellow body near the ventral surface of the kidney; at its 

 anterior end it is closely attached to the fat body. Within 

 the testis is formed the seminal fluid, containing the male 

 sex cells or spermatozoa. In the membrane which sup- 

 ports the testis note the vasa efferentia, a number of deli- 

 cate tubes leading from the testis to the inner margin of the 

 kidney; here they enter a longitudinal canal in the kidney, 

 and from this canal the seminal fluid reaches the ureter by 

 way of the urinary tubules in the kidney. Thus in the male 

 frog, the ureters function also as vasa deferentia. Ob- 

 serve the slight dilation of the ureter which functions as a 

 seminal vesicle. In the male of one species of frog (Rana 

 pipiens) the Muellerian duct, the homologue of the oviduct 

 of the female, persists as a conspicuous tube extending for- 

 ward laterally from the cloaca. In the males of most forms 

 this is represented by a mere rudiment or is absent entirely. 



In the female observe: (a) The ovaries, usually large 

 organs, filled with eggs and especially well developed dur- 

 ing the breeding season. Observe the relation of the ovaries 

 to the fat bodies and the manner in which the ovaries are 

 suspended in the body cavity. Notice the thin membrane 

 (peritoneum) that covers the ovary and is continued into 



