2 THE PHENOMENON OF 



most profitable and most promising field of action in 

 natural history; and the remarks offered here belong 

 to this field, for they discuss a general question which 

 is not foreign to any special history of development. 



Among the most essential and general characters of 

 every course of development of a natural object, are com- 

 mencement and term, and, connected with these, youth and 

 age. Youth and Age, although falling within the sphere 

 of ordinary human direct experience of life, do not appear 

 to me, in reality, so easily or simply comprehensible in 

 their true meaning and their contrasted relations, as 

 might seem from a mere abstract consideration. Answers 

 to the questions, so readily presenting themselves How 

 are youth and age distinguished? When does youth 

 cease, and age begin ? How do they pass into one 

 another ? Which is the more perfect condition of life ? 

 would penetrate deeply into the interconnection existing 

 among the totality of cosmical ideas. The purpose of the 

 present Essay only extends to a few reflections, based on 

 experience, on the changing relation of youth and age in 

 the course of the life-time of the individual. 



Youth and age are not mere periods of time, into 

 which life may be divided so as to allow us to say, Youth, 

 ceases here and Age begins; and one does not pass 

 gradually and continuously into the other, so that youth 

 decreases in the same ratio as age increases; a glance 

 into life rather demonstrates to us that the phenomena of 

 youth go through life side by side with those of age, in 

 the most varied conditions of exchange, not merely pre- 

 senting themselves simultaneously in various departments 

 of life, but crowding into the same region, and contending 

 there. Even the child has old teeth, destined to early 

 destruction (the milk-teeth), and young teeth (wisdom 

 teeth) appear even at a late age. Many organs have 

 already become old and lost their vitality before birth, 

 such as the gills of the Mammalia, the teeth of the 

 whale,* &c. ; lizards and snakes form a young skin 



* See Stannius, 'Lehrb. der Vergleich. Anatomic,' p. 411, on the teeth 



