GENERAL SURVEY OF THE FROG n 



mesentery, the mesovarium. Lateral to each ovary is its duct, the oviduct, a 

 conspicuous white, much-coiled tube, also supported by a mesentery, the meso- 

 tubarium. 



The male gonads, or testes, are a pair of small, oval yellow bodies situated 

 close to the dorsal body wall near the median line. The intestine must be pushed 

 away to see them. Each has a short mesentery, the mesorchium. The testes 

 have no ducts but the male reproductive elements pass to the exterior 

 through the ducts of the kidneys, which will be identified in the next section. 

 In our common species of frog, Rana pipiens, the male possesses a vestigial 

 oviduct, a distinct though small white tube running along the lateral border 

 of each testis. 



Attached to the anterior end of each testis, and in a similar position in the 

 female frog, is a fat body, consisting of a tuft of yellow, finger-shaped processes. 

 This organ is a storehouse for nutritive material, and its size varies with the 

 physiological condition of the frog, being very small in the spring and very large 

 in the fall before hibernation begins. 



5. Excretory system. It is composed of a pair of kidneys and their ducts. 

 Turn all of the abdominal viscera to the right, and follow the peritoneum along 

 the left lateral wall of the coelome around to the dorsal side. Note that the 

 peritoneum leaves the body wall dorsally and stretches as a thin membrane 

 across the dorsal side of the body cavity, leaving a large space between itself 

 and the muscles of the dorsal wall. This space is called the subvertebral lymph 

 sinus, or cisterna magna, and, like the subcutaneous lymph spaces, it is a part 

 of the extensive lymphatic system which the frog possesses. Within the cisterna 

 magna, certain structures, including the kidneys, are located. Such structures 

 are said to be retro peritoneal, i.e., they lie behind the peritoneum. Break 

 through the peritoneum which forms the ventral wall of the cisterna magna, and 

 locate in the cavity of the cisterna magna the kidneys, a pair of elongated, flat, 

 red bodies situated close to the peritoneum, which passes across their ventral 

 faces. From the lateral posterior edge of each kidney arises its duct, the ureter, 

 or Wolffian duct, which empties into the large intestine. The ureters not only 

 carry the urine from the kidneys to the exterior, but also transport the male 

 reproductive elements. Owing to this close connection which exists between the 

 excretory and reproductive systems in all vertebrates, the two systems are com- 

 monly referred to as the urinogenital system. The urinary bladder, although 

 functionally a part of the excretory system, is morphologically a saclike out- 

 growth of the ventral wall of the large intestine. 



6. Glands of internal secretion. Under this head are gathered together a 

 number of glandlike bodies which secrete into the blood certain substances of 

 very great physiological importance. The adrenal gland forms a bright yellow 

 stripe on the ventral face of each kidney. The spleen, which may be a gland of 



