EVOLUTIONS OF ORGANIZATION. 29 
circumstances of geological change been most active 
since then, and passed from piscine forms on to 
man. And neither the structure nor the intellect 
of man surpasses now the perfection that it had 
reached in ancient Egypt and in Greece; though 
the lapse of time has proved sufficient for varia- 
tions and degenerations. The definite lines of 
development on which the head had gradually 
risen to the perfection exhibited by the classic 
sculptors are incapable of being carried further: 
the face is curved in under the skull so far that 
it could not be carried back to a greater extent, 
and leave room for teeth, tongue, and throat. 
Nor can attention be too frequently directed to the 
ordered and completed evolution seen in the history 
of the heart, a remarkable series from the simple to 
the complex, but showing in the amphibian and 
reptilian stage a more complex mechanism, yet less 
perfect machine than in the fishes, so that, as I have 
elsewhere said, “it might have been difficult to 
explain if it could have been noted by an observer 
before birds and mammals appeared on the earth.”* 
But the mechanism gradually developed is com- 
pleted, with variety, in the bird and mammal, 
and shows no sign of undergoing further com 
plication. 
1 Animal Physiology, p. 116. 
