322 STUDIES, SCIENTIFIC AND SOCIAL chap. 



produce them, and no other cause can be suggested which 

 would." 



This assertion, that " butting with the forehead would 

 produce them," assumes the whole question at issue. 

 There is, I believe, no evidence of it whatever, and there 

 is much that renders it improbable. And the first part of 

 the statement is also erroneous, for Darwin tells us, " In 

 various countries horn-like projections have been observed 

 on the frontal bones of the horse ; in one case described 

 by Mr. Percival, they arose about two inches above the 

 orbital processes, and were very like those of a calf from 

 five to six months old, being from half to three quarters of 

 an inch in length." As no known animal in the an- 

 cestral line of the horse had horns, these must have been 

 " new characters " ; and had they appeared before the 

 ancestral horses acquired such powerful weapons of offence 

 in their hoofs, they would probably have been preserved 

 and increased by selection into formidable weapons. 

 That horns have not unfrequently arisen from such ap- 

 parently uncaused variations, is indicated by the remark- 

 able difference of structure and growth in the horns of 

 such nearly allied groups as the deer and the antelopes, 

 which at a quite recent epoch must have originated 

 independently. Very suggestive is the curious enlarge- 

 ment of the skull under the crest of the Polish fowls. In 

 another fowl's skull, figured by Darwin, there are two 

 large rounded knobs on the forehead, forming perfect 

 incipient horns. 



Dermal appendages, which could not have been caused 

 by special irritations, are so frequent, that almost any 

 useful development appears possible. The spines of the 

 hedgehog and the quills of the porcupine, are of this 

 nature, as are the plates of the armadillo and the scales of 

 the pangolin. The feathers of birds are one of the most 

 marvellous of these developments which, when they once 

 arose, were preserved and modified in endless ways. So, 

 the curious erectile appendage on the forehead of the 

 South American bell-birds, and the equally strange feather- 

 covered cylinder pendent from the throat of the umbrella- 

 birds, are other illustrations of these abnormal outgrowths 



