THE FIRST FOOD OF THE COMMON WHITE-FISH. 



(COREGONUS CI.UPEIFORMIS, Mitcll.) 



Bv S. A. FORBES. 



In a very lartre lake the conditions of life are remarkably uni- 

 form. The volume of water remains, of course, nearly constant 

 from season to season and from year to year, and the extremes of 

 summer heat and winter cold have but a moderate effect upon the 

 temperature of the lake as a whole. Consequently both plant 

 and animal life exhibit there a regularity and stability which are 

 in remarkable contrast to their fluctuations in smaller bodies of 

 water and on the surrounding land. Not only do the relative 

 numbers of individuals in the various species remain about the 

 same, but the absolute number of each must necessarily change 

 but little, as a rule. 



Such a state of affairs is eminently favorable to an exact and 

 economical balance of supply and demand, of income and ex- 

 penditure, of multiplication and destruction, among the inhabit- 

 ants of the lake. Here, every species of animal, whether preda- 

 ceous or vegetarian, must find, in the surplus products of growth 

 and reproduction among the species upon which it depends for 

 food, a far more constant and unvarying supply foi' its needs than 

 elsewhere; and the species fed upon must be subject to a far 

 more regular drain upon their surplus numbers or unessential 

 structures. Where there is little fluctuation there is little waste. 



A system of life like this, running on with relatively even tenor 

 for centuries, must of course be much less flexible than one where 

 wide and violent fluctuation and continual readjustment are the 

 rule; and a species in any way deeply affected will here 

 have within itself far less recuperative power than one which has 

 been forced again and again — each year, perhaps — to rally 

 against the most destructive attacks as the price of its continued 



