Prologue: Why Study Vertebrates? 7 



its similarity to the corresponding region of a fish. From such facts as 

 these was derived the "law of recapitulation" which, assuming evolu- 

 tion, asserts that "ontogeny repeats phylogeny" — that is, an early 

 embryo produces structures which are inherited from successive re- 

 mote ancestors, even though these structures are destined to be, in 

 later development of the embryo, either obliterated or transformed. 

 The present-day student of biology finds vertebrate anatomy par- 

 ticularly rich in opportunity for making direct acquaintance with well- 

 established facts illustrating important principles and theories of the 

 science. 



