GERMINAL SELECTION 133 



of a character. What labour and painstaking investigation it has 

 cost to give a verdict as to this even in a few instances! Innumerable 

 characters appear indifferent, and are nevertheless adaptations. Darwin 

 in his day pointed out the need for caution in this matter, referring to 

 the case of animal coloration as an example ; very little attention had 

 been directed to it for a long time because it had been believed to be 

 without significance. And how many diverse kinds of characters 

 among animals and plants, which had likewise been regarded as 

 'purely morphological,' have on more careful investigation shown 

 themselves of very great biological importance. I need only refer to 

 the shape, position, hair-arrangement, colour, and lustre of flowers, 

 and their relation to cross-fertilization by means of insects, or to the 

 thickness and shape of the leaves of tropical trees with their coating 

 of wax and their gutter-like outlets for carrying off the tropical rain 

 which falls in terrible downpour (Haberlandt, Schimper), or to the 

 limp, perpendicular drooping of the tufts of the young and tender 



Fig. 107, C. Leptoeephalus stage of an American Eel, with seven pigment 

 spots, of which three are on the left {I) and four on the right (r) side. After 

 Eigenmann. 



leaves of the same trees, which also secures protection from being 

 battered and torn by the rain. 



There are even characters the biological use of which is unknown 

 to us, but in regard to which we can affirm that they have a use. 

 Thus Eigenmann described the larva of an American eel, which differs 

 from other so-called ' Leptocephali ' in that a row of seven black spots 

 runs along its side. Apparently all these lie upon the side turned towards 

 us, but in reality they are distributed on both sides, three lying on the 

 left and four on the right, and so arranged that they look like a single 

 row of spots at regular intervals, for the flat little fish is absolutely 

 transparent. The habits of this larva are not yet known, but we may 

 conclude that this appearance of a simple row of spots must have some 

 value for the animal, for such a significant asymmetry could not have 

 arisen for purely internal reasons (Fig. 107, C). It is possible that the 

 fish is thus made to resemble parts of some marine alga, and that it is 

 thereby protected from many enemies ; that there is not a complete 



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