32 ANIMAL COLORATION. 



vantage of a green colour to tree-frequenting animals, it is not 

 a little remarkable not to meet with green in some of the 

 smaller arboreal mammals. The sloth, it is true, has greyish 

 green hair, and there are monkeys in which the fur has a 

 greenish tinge; but there is nothing like the leaf-green colour 

 of the Iguana or Phyllornis. These facts show in a very 

 striking way the limitations of the action of natural selection. 

 The colours of the mammals are mainly due to the presence 

 or to the absence of pigment in the hair; the hair is white when 

 it contains air and no pigment, or very little pigment. There 

 are apparently rarely structural peculiarities in hair which can, 

 in conjunction with the contained pigment, give rise to brilliant 

 colours. The (Jape Golden mole (Ghrysochloris) appears to 

 be one of the few exceptions, and it is remarkable that this 

 exception should be found in an animal which passes the 

 greater part of its time underground. 



The Colours of Deep-Sea Animals. 



One of the most remarkable biological discoveries of the 

 last thirty years is the proof that animals can live in the deep 

 abysses of the ocean. The first actual demonstration of this 

 truth appears to have been made so long ago as the year 1818, 

 during the Arctic voyage of Sir John Ross ; from a depth of 

 800 to 1000 fathoms an Astropkyton was brought up on the 

 sounding line; but little attention, however, was paid to the 

 matter until the cruise of the Lightning and the Porcu- 

 pine, in the years 1801-70. Since that date the memorable 

 Challenger expedition, and numerous other expeditions fitted 

 out by foreign governments, have resulted in the acquirement 

 of a vast amount of knowledge about the inhabitants of the 

 deep waters. 



Next in importance to the actual proof that animals, differing 



