282 



ELEMENTARY BIOLOGY 



b d 



Fish, Chinook salmon (Oncorhynchus tschawytscha) 



Batrachian, frog (Rana palustris) 



Batrachian, newt (A mblystoma punctatnm) 



FIG. 1 1 8. Development in some backboned animals 



a, egg; a^ fish ready to break out of egg; l>, first free-swimming stage (tadpole in 

 batrachians) ; b-, later stage in fish, still showing yolk sac ; <:, more advanced stage (in 

 batrachians, tadpole just before the appearance of hind legs) ; J, later stage ; e, adult form 



during the three weeks of hatching something was going on 

 inside the eggshell of the chick. 



The development of an individual through a series of 

 well-marked stages is called a metamorphosis, which means 

 " trans-formation." 



