92 EVOLUTION 



sacrifices in maternity; the male relatively 

 the more disruptive, whence his usually more 

 vivid life, his explosive energies in action. 

 In short, the sexes express a fundamental 

 difference in the rhythm of metabolism. 



This initial difference not only leads to the 

 primary functional distinction between male 

 and female, but it also determines, either 

 from the start, or after maleness and female- 

 ness have been partly established, what par- 

 ticular expression will be given to a whole 

 series of secondary characters, both struc- 

 tural and functional whether a masculine 

 or a feminine expression. 



THE BEGINNINGS OF BRAINS. In most 

 sponges and coelenterates (such as jelly-fish, 

 sea-anemones and coral polyps) the body 

 has radial symmetry. That is to say, it is 

 the same all round, it has no right nor left, it 

 can be cut into symmetrical halves along 

 many different vertical planes. This kind of 

 symmetry is well suited for sedentary life, 

 like that of sea-anemones, which wait for 

 food to come within the scope of their sting- 

 ing and grasping tentacles; or for an easy- 

 going life, like that of jelly-fishes, which live 

 in the very uniform environment of the open 

 sea where all directions mean very much the 

 same, 



