208 ELEMENTARY BIOLOGY. [CHAP. 



with the season of the year. The numerous 

 ova in it. 



/3. The oviduct: a convoluted tube, not con- 

 tinuous with the ovary, and running back to 

 open into the cloaca. The greater part of 

 the oviduct is opaque and glandular; the 

 part near the cloaca however is dilated, thin- 

 walled and transparent. The oviducts open 

 on the posterior wall of the cloaca a little 

 anterior to the openings of the ureters. 



ii. The mouth, oesophagus, and respiratory organs. 



a. Open the mouth : note on its roof near the front 

 the two hinder openings of the nasal cavities 

 (posterior nares]\ farther back, the two larger 

 openings of the Eustachian recesses; the long 

 tongue in the floor of the mouth; fixed by its 

 front end to the lower jaw; its free bifid end 

 turned towards the throat. 



b. Enlarge the mouth-opening by cutting through 

 the sides of the buccal cavity with a pair of 

 scissors : pull down the lower jaw so as to see 

 the chamber (pharynx] behind the mouth. 



c. On the floor of the pharynx is a narrow opening 

 (the glottis) : pass a probe down it through the 

 larynx and very short trachea into the lungs. 



d. Remove the lungs ; open one ; it is a thin-walled 

 cavity with a sacculated inner surface. 



e. Trace the oesophagus up to the pharynx. 



C. THE CIRCULATION OF THE BLOOD IN THE FROG'S WEB. 



i. Get a piece of thin board, about 5 inches long 

 and 2\ broad ; in the middle of one end of it cut 



