Chap. IX. 
SEXUAL SELECTION. 
323 
protection ; but when we are reminded by Hackel that 
not only the medusae but many floating mollusca, crus- 
taceans, and even small oceanic fishes partake of this 
same glass-like structure, we can hardly doubt that 
they thus escape the notice of pelagic birds and other 
enemies. 
Notwithstanding our ignorance how far colour in 
many cases serves as a protection, the most probable 
view in regard to the splendid tints of many of the 
lowest animals seems to be that their colours are the 
direct result either of the chemical nature or the minute 
structure of their tissues, independently of any benefit 
thus derived. Hardly any colour is finer than that of 
arterial blood ; but there is no reason to suppose that 
the colour of the blood is in itself any advantage ; and 
though it adds to the beauty of the maiden’s cheek, no 
one will pretend that it has been acquired for this pur- 
pose. So again with many animals, especially the lower 
ones, the bile is richly coloured ; thus the extreme 
beauty of the Eolidae (naked sea-slugs) is chiefly due, as 
I am informed by Mr. Hancock, to the biliary glands 
seen through the translucent integuments ; this beauty 
being probably of no service to these animals. The 
tints of the decaying leaves in an American forest are 
described by every one as gorgeous ; yet no one sup- 
poses that these tints are of the least advantage to 
the trees. Bearing in mind how many substances 
closely analogous to natural organic compounds have 
been recently formed by chemists, and which exhibit 
the most splendid colours, it would have been a strange 
fact if substances similarly coloured had not often 
originated, independently of any useful end being 
thus gained, in the complex laboratory of living 
organisms. 
