44 GENERAL BIOLOGY 



spiracle found? At this stage the eye, mouth, nostrils and 

 teeth are well developed. Also on the ventral surface the 

 heart, internal gills, and coiled intestine will show through 

 the body wall. 



8. Metamorphosis. The tadpole or fish-like stage con- 

 tinues for some time (it may be a year or two in frogs) be- 

 fore a metamorphosis into the adult form begins. This 

 metamorphosis is first shown by the formation of the hind 

 legs. Carefully study a tadpole with the hind legs present 

 and determine the character of sense organs and other ex- 

 ternal features. The forelegs start their formation within 

 the gill chamber and are not apparent externally until 

 they become rather large, when they break through the 

 skin covering the gills. In a specimen with both fore and 

 hind legs observe the changes in form of the body and head. 

 As the legs increase in size what becomes of the tail? 



Dissect the ventral body wall from a large tadpole with- 

 out legs, and also from one with both pairs of legs present. 

 Determine what changes are taking place in the internal 

 organs during this time. When the tail is finally absorbed 

 and the toad or frog leaves the water, the animals are like 

 adults except for the reproductive organs, which require 

 a considerable time for their perfect development. 



