viii 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 hinted, 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 that 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- 



