BULLFROG AS TYPICAL VERTEBRATE ANIMAL 



95 



Sound progresses in the following fasliion. The tympanic mem- 

 brane vibrates to sound waves, and these are transported by the 

 columella to the inner ear. These vibrations are taken up by the 

 endolymph of the saceulus and are received by the nerve endings 

 which lead to the auditory nerves. These nerves convey the im- 

 pulse to the brain, subsequently giving rise to auditory sensations. 



In a similar manner, movements of the endolymph in the utricu- 

 lus affect sensory cells and cause a reaction associated with a sense 

 of position or equilibration. 



Fig. 31. — The right internal ear of the frog, lateral view. 



Reproductive Organs 



The ovoid testes of the male bullfrog are attached to each kidney 

 by a fold of peritoneum, the mesorchium. In this fold, running be- 

 tween the testes and kidneys, are several small ducts, the vasa ef- 

 ferentia. These ducts connect with the mesonephric duct through 

 Bidder's canal and the collecting tubules of the kidney. Spermatic 

 fluid containing the spermatozoa passes from the testes through the 

 vasa efferentia into the kidney, then into the mesonephric duct, which 

 opens into the cloaca, and thence to the outside through the anus. In 

 some species, this duct is slightly expanded prior to its opening into 

 the cloaca to form the seminal vesicle, a reservoir for spermatozoa. 

 This is poorly developed in the bullfrog. 



The two ovaries of the female bullfrog, when filled with eggs, 

 occupy a large part of the body cavity and consist of folded sacs 

 covered with peritoneum. They originate in about the same posi- 

 tion as do the testes and lie in a fold of the peritoneum, mesovarium, 

 ventral to the kidneys. 



