viil INTRODUCTION. 
completed, the evolution ceases, although, by the 
operation of environment or external circumstances, 
variations may continue to occur and degenerations 
of diverse kinds may take place. 
Such views demand for the universe a back- 
ground or underlying element of spirit. Among 
the evidences of the place occupied by spirit in 
nature, I count that which is afforded by what I 
term symbolic correlation as highly important, and 
the demonstration of the existence of symbolic cor- 
relation I have sought to establish by an analysis of 
human expression. At the conclusion of the article 
on that subject the existence of such a principle of 
expression as conducing to the characters of biolo- 
gical evolution is simply hintéd, while it is referred 
to more fully, but still with great brevity, in the 
first article of the series. 
Under the head of “‘ Vision” it is shewn that the 
evolution of sense-organs is a very different thing 
from the evolution of sensation; and while it is 
pointed out that natural selection furnishes no 
adequate explanation of the rise of the. organ of 
vision as a structure, attention is called to the cir- 
cumstance thgt the very existence of vision and the 
other senses points to there being an unknowable 
territory whence, and not from the material world, 
they take their origin. 
In discussing the subject of vision, the whole sub- 
ject of sensation has naturally come up, and refer- 
