TRANSLATOR'S PREFACE 



be indifferent or disadvantageous to the attainment of the 

 useful result. As far as we can judge, all the specific mark- 

 ings are indifferent. And the change of colour is far less 

 important than is generally supposed. The soles in aquaria 

 are nearly always buried in the sand on which they live : 

 they come out most at night, when to our eyes at least no 

 colours can be distinguished ; and when they move about to 

 seek food in the day-time, they are almost always covered by 

 a thin layer of sand sprinkled over their upper sides, by 

 which their colour is concealed. 



Again, the lower sides of flat fishes are, except in rare 

 abnormal specimens, of a uniform opaque white, and it is 

 impossible to conceive any advantage which they could 

 derive from this, since the lower sides are usually concealed. 

 It is true that plaice and flounders often rise a short distance 

 from the bottom to seize food ; and in this condition their 

 white lower sides are very conspicuous. 



The peculiar structural condition of the flat fishes as 

 compared with symmetrical fishes is admitted on all sides to 

 be one of the most striking cases of adaptation that exist. 

 Yet so obvious is the conclusion that the evolution of the 

 asymmetry is due to the habits of the fishes, that Mr. 

 Wallace, in his new book on Darwinism, attributes the 

 distortion of the orbits to the efforts of the ancestral flat 

 fishes during innumerable generations, at the very moment 

 when he is repudiating with Weismann the inheritance of 

 acquired characters. When it is pointed out that he is thus 

 using the very principle which he denies, he justifies himself 

 by the sophistry that what was selected in successive genera- 

 tions of flat fishes was the power in the skull of retaining 

 the distortion which the efforts of the muscles produced. 



