ASSIMILATIVE COLOURATION. 389 
in the lives and development of these creatures, connected and 
increasing with an advancing animal evolution, but still only a 
term to express the modifying influences incidental to a struggle 
for existence.* In fact, natural selection is more an effect than 
a cause. It was incidental and consequent to the progress of 
evolution in animal life, and ever increasing its sway in ratio 
with the vast increase of living things became the giant modi- 
fying influence, and modelled, painted, exterminated, and sus- 
tained the fauna and flora which by their dangerous fecundity 
came under her rule. But because a phenomenon is ancient it is 
not necessarily eternal—theologians discuss those questions— 
and if logic imperatively demands an antecedent to natural 
selection, biology must refuse to recognize that undoubtedly 
mighty and modifying influence as a First Cause.t ‘‘ We attach 
too exclusive an importance to adaptation . . . when we think 
to explain by selection every similarity between the colouring of 
an animal and that of the ground on which it lives. For, as we 
have seen, animals may become similar in colour to their sur- 
roundings, actually adapted in colour, quite by chance; for 
instance, in consequence of the direct necessary action of light, 
4.@ of the surrounding colours, and therefore without selection, 
many really wonderful cases of adaptation, apparently due to 
selection, probably come under the category.’’} 
It seems a probable suggestion that assimilative colouration 
was a very constant factor in an early stage of animal life, and 
* To understand the philosophical conceptions in Biology previous to 
the Darwinian epoch, which may be said to have commenced with the pub- 
lication of the ‘Origin of Species’ in 1859, we may with the greatest in- 
struction reperuse the ‘Essay on Classification,’ written by that master 
naturalist, Agassiz, the preface of which bears date 1858, the same year that 
simultaneous papers by Darwin and Wallace were read before the Linnean 
Society, and the way made straight for the theory of natural selection. In 
the essay of Agassiz only three references are made to Darwin, and those 
purely bibliographical, recording more or less technical memoirs. In a 
philosophic sense the ‘ Essay on Classification ’ may be described as the last 
charge of the Old Guard. 
+ It will be remembered that Mr. Mivart has brilliantly advanced his 
thesis that ‘‘species have been evolved by ordinary natural laws (for the 
most part unknown) aided by the swbhordinate action of‘ natural selection’”’ 
(‘ Genesis of Species,’ p. 333). 
t Eimer, ‘ Organic Evolution,’ Eng. transl. p. 144. 
