68 ON PLANTS AND INSECTS. [LECT. n. 



caterpillars, which at first sight seem so fantastic and 

 inexplicable. I should, however, produce an impression 

 very different from that which I wish to convey, were I 

 to lead you to suppose that all these varieties have been 

 explained, or are understood. Far from it ; they still 

 offer a large field for study ; nevertheless I venture to 

 think the evidence now brought forward, however 

 imperfectly, is at least sufficient to justify the con- 

 clusion that there is not a hair or a line, not a spot 

 or a colour, for which there is not a reason, which has 

 not a purpose or a meaning in the economy of nature. 



