n6 THE EVOLUTIONIST AT LARGE. 



another pair installed in their place to- 

 morrow. Young fry seem always ready to 

 fill up the vacancies caused by the involun- 

 tary retirement of their elders. Their size 

 depends almost entirely upon the quan- 

 tity of food they can get ; for an adult fish 

 may weigh anything at any time of his life, 

 and there is no limit to the dimensions 

 they may theoretically attain. Mr. Herbert 

 Spencer, who is an angler as well as a 

 philosopher, well observes that where the 

 trout are many they are generally small ; and 

 where they are large they are generally few. 

 In the mill-stream down the valley they 

 measure only six inches, though you may fill 

 a basket easily enough on a cloudy day ; but 

 in the canal reservoir, where there are only 

 half-a-dozen fish altogether, a magnificent 

 eight-pounder has been taken more than 

 once In this way we can understand 

 the origin of the great lake trout, which 

 weigh sometimes forty pounds. They are 

 common trout which have taken to living 



