CHAPTER VII 

 METAMORPHOSIS AND RECAPITULATION 



As one of the most remarkable examples of meta- 

 morphosis and recapitulation in connexion with 

 adaptation we will consider once more the case 

 of the Flat-fishes which I have already mentioned 

 in an earlier chapter. These fishes offer perhaps 

 the best example of the difference between gameto- 

 genic mutations and adaptive modifications. In 

 several species specimens occur occasionally in 

 which the asymmetry is not fully developed. 1 

 These abnormalities are most frequent in the 

 Turbot, Brill, Flounder, and Plaice. The chief 

 abnormal features are pigmentation of the lower 

 side as well as of the upper, the eye of the lower 

 side, left or right according to the species, on the 

 edge of the head instead of the upper side, and the 

 dorsal fin with its attachment ceasing behind this 

 eye, the end of the fin projecting freely forwards over 

 the eye in the form of a hook. Such specimens have 

 been called ambicolorate, but it is an important fact 

 that they are also ambiarmate that is to say, the 

 scales or tubercles which in the normal Flat-fish are 

 considerably reduced or absent on the lower side, in 

 these abnormal specimens are developed on the 

 lower side almost as much as on the upper. Minor 



1 See 'Coloration of Skins of Fishes, especially of Pleuronectidao,' 

 Phil. Trans. Royal Soc., 1894. 



198 



