4 REPRODUCTION 



whole life period of an animal is long, its immaturity is 

 likely to be long; if the youth is short, the life is likely to 

 be short. 



Organisms frequently pass through striking changes in 

 appearance during this period of immaturity. The word 

 larva suggests some of these. The immature (larval) 

 butterfly is not like a butterfly, but is a worm-like 

 caterpillar; the immature frog does not look like the adult, 

 but has a tail and gills, as a fish has. The leaves of the 

 seedling plant are very different from those of the old 

 plant. This period is very important in many other 

 organisms beside man. It is the formative period. The 

 expression "as the twig is bent the tree inclines," expresses 

 a general law of life. The growth period is the great time 

 of adjustment. It is the period in which the individual 

 gets a chance to make its adjustments to the important 

 conditions of its life. Later, when the individual is full 

 grown, changes or adjustments are made with difficulty, 

 if at all. But in its youth and growth the individual is 

 plastic; that is, it can be modified without injury better to 

 fit its environment. 



So, in human beings, youth is the time for education, the 

 time of the formation of habits and of character. What 

 you may learn without difficulty now may be much more 

 difficult when you are older. Youth, then, is the great 

 period of opportunity, as well as the period of growth. 

 Fortunate indeed is the boy or girl who fully realizes this, 

 and makes the most of youth's rich opportunities before 

 it is too late. 



6. Maturity. At maturity a plant or animal comes to its 

 full powers, size, and nature. At this stage the increase 

 is no longer greater than the outgo. They just about 

 balance. The length of time that this is true also varies 

 greatly in different kinds of organisms. Some begin to 

 decline in a few days or weeks after becoming mature. 

 This is true of a great many insects. In others there may 



