THE PEACOCK'S TRAIN 307 



gress being lost first, and then the step which preceded 

 that, and so on. So that the "degenerating" or " retro- 

 gressing " animal, or plant, or human race, must go 

 steadily back on the very path by which its race 

 previously advanced, passing in reverse order through 

 the stages of its former progress. I know of no evidence 

 for this. The simplifying process shown in specialised, 

 quiescent, well-fed animals, or in parasites, does not 

 proceed backwards by the same steps or along the same 

 path by which previous progress was made. The special 

 development of some dominating organ or character is 

 the central feature of the simplifying process, and affects 

 all the degenerative changes which take place. They 

 are not repetitions in the reversed order of the former steps 

 of progress, but new arrangements of the whole organism. 

 An instructive and typical case of simplification with 

 specialisation is seen in certain feathers of the peacock's 

 " train " (a tail which is not formed by the true tail 

 feathers, but consists of the enlarged tail " coverts " or 

 covering feathers, the true tail quills of a dull brown 

 colour forming a separate group hidden from view by the 

 gorgeous coverts). The ordinary feathers of the peacock's 

 body are small, symmetrical feathers, with simple colouring. 

 We find near the peacock's tail a series of feathers which 

 are intermediate steps, leading on gradually in colour, size, 

 and shape from the simple " coverts " of the body to the 

 great eye-bearing, metallic-looking feathers of the " train " 

 which the bird raises in display. The feathers which 

 constitute these intermediate steps have the two sides 

 right and left of the shaft equal, and show a series of 



PLATE XII. Photographs of a series of feathers from the back and covering 

 feathers of the peacock's " train " showing from above downwards the 

 gradual increase in size and the development of the " eye " and coloured 

 rings of the larger feathers. From a preparation placed by Sir William 

 Flower in the central hall of the Natural History Museum. 



