*n PHYLUM CHORDATA 427 



handle united to the stapes, a nodule of cartilage which is 

 fixed in the membrane of the fenestra ovalis (p. 358). 

 Sonorous vibrations striking the tympanic membrane are 

 communicated by the columella and stapes to the fenestra 

 ovalis, thence to the perilymph, and thence to the mem- 

 branous labyrinth. The connection of the Eustachian tube 

 with the mouth obviates undue compression of the air in 

 the tympanic cavity. 



The kidneys (Figs. 251 and 253, Kd, and Figs. 256 

 and 257, N) are flat, somewhat oval bodies of a dark 

 red colour, lying in the posterior region of the ccelom. 

 On the ventral face of each is an elongated, yellow adrenal, 

 and irregularly scattered nephrostomes occur on the same 

 surface. They do not, however, communicate with the 

 urinary tubules, but with the renal veins, and serve to propel 

 the lymph from the coelom to the venous system. The 

 ureters ( Ur) pass backwards from the outer borders of the 

 kidney, and open into the dorsal wall of the cloaca ( Cl) . 



Opening into the cloaca on its ventral side is a bilobed, 

 thin-walled, and very delicate sac, the urinary bladder (Fig. 

 251, </), into which the urine passes by gravitation from 

 the cloaca when the anus is closed. 



The testes (Fig. 256, Ho) are white ovoid bodies lying 

 immediately ventral to the anterior ends of the kidneys, to 

 which they are attached by folds of peritoneum. From the 

 inner edge of each pass a number of delicate vasa efferentia, 

 which enter the kidney and become connected with the 

 urinary tubules. The spermatic fluid is thus passed into 

 the urinary tubules and carried off by the ureter, which is 

 therefore a urinogenital duct in the male frog. A vesicula 

 seminalis opens by numerous small ducts into the outer side 

 of the ureter. Attached to the testis are lobed bodies of a 

 bright yellow colour, the fat-bodies (FK) . 



