THE KINSHIP OF LIFE, 35 
of heredity. If, however, man possessed no “ blood re- 
lationship ” to three-eyed vertebrates, the existence of 
Fic. 3.—Head of the lizard, or “horned toad” (Phrynosoma blani- 
willet), 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. 
