How Theories are Manufactured 99 



stripes often follow the lines of the spine and ribs, the 

 shoulders and hips are marked by curved lines, and 

 emphatic coloration picks out the extremities of ears, 

 feet, and tail. Among insects the same sort of thing 

 is noticeable. In butterflies, the spots and bands 

 usually have reference to the form of the wing and the 

 arrangement of the nervures. Even in birds the dis- 

 tribution of colour and markings follows generally the 

 same law. The crown of the head, the throat, the ear- 

 coverts, and the eyes have usually distinct tints in all 

 highly-coloured birds, and distinct patches of colour are 

 frequently situated on special centres of muscular action, 

 as on the breast and the root of the tail. Mr. Wallace 

 also points out that special brilliance of coloration often 

 accompanies other symptoms of more than ordinary 

 vigour. "Brilliant colours," he says, 1 "usually appear 

 just in proportion to the development of tegumentary 

 appendages. Among birds the most brilliant colours 

 are possessed by those which have developed frills, 

 crests, elongated tails, expanded wings, or plumes," 

 like the Humming-birds, Peacock, Argus Pheasant, or 

 Birds of Paradise respectively. So, too, among insects 

 the most gaudy are those which have the most expanded 

 wings, as Butterflies, Moths, and Dragon-flies. 



Here is an interesting collection of facts if, indeed, 

 the general proposition itself be a fact 2 but what then? 

 Where is the " explanation " of coloration which these 

 facts afford? Apparently we are to understand that 

 vital vigour produces colour, and that where the former 



1 P. 290. 



2 The fact for which Mr. Wallace contends .seems to require large 

 deductions. Among birds the ornamental bars of the wings and 

 tail generally run across the line of their structure and do not follow 

 it. Moreover, the most beautiful effects are produced by differences 

 of hue in each individual feather. Our brightest British Birds, as 

 the Kingfisher and the Goldfinch, develop no crests or appendages. 

 The Pheasant develops a long tail, but it is sombre in colour in 

 comparison of the neck and back. Moreover, the theory seems to 

 deal only with brilliant coloration and to afford no explanation of 

 the not less beautitul effects produced by delicate shading, as in the 

 Woodcock or Partridge. 



