A SURVEY OF THE LATER EMBRYO OR LARVA 159 



tion of the tadpole into the frog. The larval skin is shed, along with 

 the horny jaws. The mouth becomes a large horizontal slit instead 

 of a simple oval opening. The gill clefts are all closed. 



There is thus developed a frog in miniature, once metamorphosis 

 is achieved and the embryonic stages of development are passed. It 

 will be necessary now to return to the earlier developmental stages 

 and treat the various derivatives of the three primary germ layers. 

 The student is cautioned not to lose sight of the fact that the embryo 

 is a composite whole, even though we are discussing the development 

 of one or another of the various systems. There is functional inte- 

 gration which must be implied, while we are studying an isolated 

 system in detail. 



