340 ANIMAL BIOLOGY 



of every mother. When the need for milk and protection 

 is past parental affection as a rule soon passes into indiffer- 

 ence. The period of relatively helpless infancy increases 

 as we pass to higher mammals. This affords a greater 

 opportunity to learn by experience while under the pro- 

 tection and guidance of parents before the young animal 

 has to face the serious business of life. Young birds are 

 taught to fear particular enemies and to peck at certain 

 kinds of food. The danger chirr of the old hen fills the 

 young chick with alarm and the alarm notes of the par- 

 tridge will send the young into hiding places in the grass. 

 The lessons learned in infancy frequently are the means 

 of saving life when the young are free from parental 

 guidance. 



Among the simplest organisms, as we have seen, the 

 perpetuation of life is effected simply by the process of 

 fission. In somewhat higher forms we meet with phenome- 

 non of sex, and the various activities of mating. Later we 

 find that the activities of reproduction involve the care 

 of eggs and young; and as we ascend the scale of life the 

 time and energy expended upon the rearing of offspring 

 becomes greater and greater. The perpetuation of the 

 race finally comes to mean not only the production of 

 new individuals, but the fostering and training of the 

 new generation until it is capable of leading an independent 

 life. 



