262 ANIMAL BIOLOGY 



biological and physiological contrast of individuals that bear sperm 

 and eggs respectively. Sex, indeed, becomes largely a dominating 

 factor in the life of the lower animals, and even of Man, where 

 the primary function of somatic sexual differentiation to ensure 

 fertilization appears to become largely submerged. ' It is as though 

 variety and beauty had become ends in themselves in the evolu- 

 tion of secondary sex characters, as exemplified in the plumage of 

 birds, and in the strife and amenities of human social relations." 



