Amphibia. 87 



each side of the cloaca is a flattened reddish body, the kidney. 

 The ventral face of each usually shows a yellowish streak. 



11. Near the ventral surface of each kidney, in the male frog, 

 is the white, oblong spermary. 



12. In the female, the ovary occupies a corresponding posi- 

 tion ; but often the ovaries are found greatly distended by eggs, so 

 much so that they occupy the larger part of the body cavity. The 

 eggs are black and white. The ovaries are held within the two 

 folds of the mesentery, hence, when distended with eggs, they 

 present a much folded and plaited appearance. The oviducts are 

 long, convoluted, whitish tubes, occupying considerable space in 

 the dorsal part of the body cavity on each side. With fine scissors 

 make a small slit in one of the oviducts near the posterior end, 

 and insert a dark bristle to find the opening into the cloaca. 

 Make a similar opening near the anterior end of the oviduct and 

 probe to find the opening by which the eggs enter the duct at its 

 free end in the body cavity near the base of the lung. 



13. Connected with the ovaries and spermaries are usually 

 several finger-like masses of yellow fat. 



14. Close to the anterior end of the cloaca is the small, red, 

 spherical spleen. 



15. In the extreme posterior end of the body cavity is the 

 urinary bladder. It is a thin, delicate sac, which is usually found 

 empty, and floats upward in the water like a mere fold of nearly 

 transparent membrane. Insert the blowpipe through the anus 

 and inflate. This should reveal its shape and size, if it has not 

 been perforated. 



The Circulation of Blood in the Web of a Frog's Foot. For 

 this get a frog with a pale web. Take a piece of shingle six inches 

 long and three inches wide. Cut a round hole, half an inch in 

 diameter, near one end of it. Wrap the frog in a wet cloth, with 

 one leg projecting, and tie it, thus wrapped, to the shingle. Tie 

 threads around two of the toes, and stretch the web, but not too 

 tightly, over the hole. Place the shingle firmly on the stage of a 

 microscope. Examine first with a low power. The large tubes 



