CHAPTEK IV 



VEETEBBATES : BACKBONE AND BBAIN 



In tracing man's ancestry from fish upward we ought 

 properly to describe three or four fish, an amphibian, 

 a reptile, and then take up the series of mammalian 

 ancestors. But we have not sufficient time for so ex- 

 tended a study, and a simpler method may answer 

 our purpose fairly well. Let us fix our attention on 

 the few organs which still show the capacity of 

 marked development, and follow each one of these 

 rapidly in its upward course. 



We must remember that there are changes in the 

 vegetative organs. The digestive and excretory sys- 

 tems improve. But this improvement is not for the 

 sake of these vegetative functions. Brain and muscle 

 demand vastly more fuel, and produce vastly more waste 

 which must be removed. At almost the close of the 

 series the reproductive system undergoes a modifica- 

 tion which is almost revolutionary in its results. But 

 we shall find that this modification is necessitated by 

 the smaller amount of material which can be spared 

 for this function ; not by its increasing importance, 

 still less its dominance for its own worth. The verte- 

 brate is like an old Eoman ; everything is subordi- 

 nated to mental and physical power. He is the world 

 conqueror. 



