THE CYCLE OF LIFE 411 



component spermatozoa. These exhibited astonishing 

 activity, and some kept it up below a cover-slip for seven 

 hours after liberation. 



Many of the lower animals feed easily and have much 

 to spare, so that they can afford to be prolific. Moreover, 

 until the nervous system reaches a certain degree of integra- 

 tion, the sexes cannot be definitely aware of one another. 

 In Echinoderms, for instance, the absence of ganglia puts 

 definite sex-awareness out of the question. At many 

 different points, however, in the ascent of life we find 

 economization of reproductive material. An incipient case 

 is familiar in the salmon. The female fish makes a furrow 

 in the gravelly bed of the river and lays her eggs there. 

 The attendant male is stimulated by the presence of the 

 mature female and her eggs, and liberates the sperms or 

 milt along the furrow. There is still great loss, but it is 

 the beginning of an improvement upon the primitive and 

 wasteful broadcast semination of the waters. 



Along various lines of animal evolution we find that the 

 males and females have become very definitely aware of 

 one another and are excited by one another. There is a 

 by-play of amatory behaviour preliminary to pairing, and 

 probably rendering the pairing more effective. A pervasive 

 excitement may change the creature's character and appear- 

 ance ; the whole being is sometimes, as it were, transfigured. 

 There is often a seeking out of the females by the ardent 

 males, and occasionally there is an appeal made to the 

 males by the females. The excited males fight with one 

 another, sometimes with almost maniacal ferocity, some- 

 times in a half-playful, bloodless jousting. Again, in a 

 fascinating variety of ways, the males make displays of 

 agility, of mettlesomeness, of beauty, of fragrance, of 



