THE KINSHIP OF LIFE. 



35 



of heredity. If, however, man possessed no " blood re- 

 lationship " to three-eyed vertebrates, the existence of 





FlG. 3. Head of the lizard, or " horned toad " (Phrynosoma blani- 

 villei], showing the translucent pearly scale covering the pineal eye. 

 From Nature, by W. S. Atkinson. 



the pineal body in the human brain would be wholly 

 inexplicable. 



It has been difficult to explain, on the theory of de- 

 scent, how complex organs like the eyes and ears of the 

 higher animals could develop from small 

 beginnings. To embryology we must 

 look for explanation. Embryology tells 

 us that these organs do not in the individual reach per- 

 fection "all at once." In every case the embryonic his- 

 tory of a highly specialized organ shows a succession of 



Origin of com- 

 plex structures. 



