410 THE WONDER OF LIFE 



experiment. The supreme duty of youth is to try all 

 things '. 



Finally youth passes into adolescence. This is an arc 

 on the up-grade, when juvenile characters are shed and 

 adult characters put on. There is a final acceleration of 

 growth (with correlated rest and play, and plenty of food) ; 

 there is internal rearrangement and readjustment ; there 

 is a sifting of idiosyncrasies, to wit variations ; there is a 

 criticism of that acquired veneer which we call modifications 

 or individually acquired characters ; and there is more 

 than a beginning of sex-impulses. 



Courtship among Animals. In the lower reaches 

 of the animal kingdom the process of reproduction is often 

 extraordinarily wasteful. Myriads of eggs are sown broad- 

 cast upon the waters, and millions of sperms are shed 

 fortuitously. Many fishes produce several millions of eggs, 

 and there is no counting spermatozoa. Mr. Oswald H. 

 Latter has given a vivid description of the discharge of 

 spermatozoa from the male freshwater mussel. It may 

 serve to illustrate the prodigal wealth of reproductive 

 material. A specimen of Unio pictorum emitted from the 

 exhalant aperture between the shell- valves a fine double 

 cloud of milky substance, which rose nearly to the surface 

 of the water, and then fell as a diffused cloud. The 

 whole of the water in the aquarium became cloudy 

 and the emission continued for some hours. It appeared 

 to be under some control, for a slight shaking of the floor 

 was followed by a cessation of the streams of spermatozoa, 

 though the ordinary exhalant current of water appeared 

 to continue without interruption. The liberated material 

 consisted of myriads of sperm-balls, revolving and swimming 

 like Vol vox-colonies, and finally breaking up into the 



