377 



FIG. 187. The metamorphosis of the Frog. (After Brehm.) Numbers indicate the 



sequence. 



Questions on the figures. How much of the egg is really ovum? 

 What are the changes which take place in passing through the various 

 stages? In what order do the legs appear? How is respiration affected 

 after stage 6? After stage n? What is proven by the collecting of the 

 tadpoles as shown in 3? How do they retain their position. 



FIG. 188. 



FIG. 1 88. Tailed Amphibians. From Nicholson, after Mivart. A, Siren; B, Am- 

 phiuma tridactyla; C, Necturus. 



Questions on the figures. Compare these three types and note all the 

 chief differences of external structure. Compare also with figures you 

 may be able to find of other Urodela. 



