SIMPLIFICATION OF TRAIN-FEATHERS 309 



or leaflets confined to one side only. A specially 

 arranged series of these feathers is shown in the Natural 

 History Museum, from which our Plates XII and XIII 

 have been produced by photography. 



Assuredly in the process of gradual transition from 

 the central fully developed eyed feather of the peacock's 

 train to the one-sided metallic simplifications at the sides 

 of the group degenerate residues of the gorgeousness of 

 the complete feather ! there has been no " retrogression " 

 in the strict sense of the word, no yielding or disappear- 

 ance step by step of characters previously developed, in 

 the order given by the phrase, " latest attained first to 

 vanish." On the contrary, the one-sidedness is a new 

 character, and is gradually increased until it is complete. 

 The large size of the feather is a late character, and is 

 retained ! The freedom of the rami of the feather from 

 adhesion to one another is a very late character, and so is 

 the metallic iridescence. Neither of these disappears. 

 Late developed and highly peculiar features are retained, 

 whilst a new and dominating specialisation that of one- 

 sidedness leads to the total disappearance of the primitive 

 characters of a covert feather, and also to the disappear- 

 ance of the shaded eye-spot and ring, which is the common 

 possession of all the larger train-feathers, and is not a late 

 step in the upward gradation. In fact, the peacock's train 

 shows us that the simplification of organic structure (spoken 

 of usually as " degeneration "), which often arises in the 

 course of evolution, as in the Ascidians, the parasitic 

 crustaceans and worms and in many groups of plants, 

 as well as of animals, is most emphatically a totally 

 different thing from a retracing of the steps of progress. 

 It is not a ' retrogression " a return along the steps of 

 previous progression but a simplification, a loss of 

 certain parts, accompanied by new dispositions and inter- 

 relations of surviving parts. 



