SUDDEN VARIATION. 169 



conditions this young he-goat may become the founder of 

 an entirely new four-horned race, or (by correlative adapta- 

 tion and constant heredity) of a new fixed species. 



But if we now search for the physiological functions of 

 evolution which have " suddenly " formed this new race or 

 species, we find that a change in the hereditary nutrition at 

 two points in the frontal bone and in the skin covering the 

 same is the prime cause. Owing to the excessive local 

 nutrition of the osseous tissue, and the consequent propor- 

 tionate multiplication of cells, a bony protuberance gradually 

 appears at each of these points; and in consequence o* 

 correlative adaptation, the hairy skin covering both these 

 protuberances, changes into a hard, bare horny sheath, 

 analogous to the other two horns which have long been 

 hereditary. As these bony protuberances grow, and their 

 horny sheaths become correspondingly larger, a new, second 

 pair of horns appears behind the old ones. All these func- 

 tions of evolution which " suddenly and by a leap " produce 

 this four-horned form of goat are in reality perfectly "gradual 

 and continuous " changes in the evolution of those masses of 

 cells of which we have spoken : they depend on a change 

 in the nutrition of the tissue at these two points in the 

 frontal bone and skin. In this instance, therefore, an accu- 

 rate examination of the physiological function of evolution 

 affords a perfectly natural explanation of an apparently 

 miraculous process. This is equally true of individual and 

 of phyletic evolution. 



This is also the explanation of a process of evolution 

 which above all others is usually put under mystical veil 

 as though it were a supernatural wonder; this is the 

 process of fertilization, or sexual generation. In all the 



