504 LAWS OF MULTIPLICATION. 



as the other. This absence of difference cannot be ascribed 

 to their unlike degrees of activity. We must seek its cause 

 in some facility of living secured to the Eat by its greater 

 intelligence, greater power and courage, greater ability to 

 utilize what it finds. The Rat is notoriously cunning; and its 

 cunning gives succe&s to its foraging expeditions. It is not, 

 like the Mouse, limited mainly to vegetal food; but while it 

 eats grain and beans like the Mouse, it also eats flesh and 

 carrion, devours young poultry and eggs. The result is that, 

 without a proportionate increase of expenditure, it gets a far 

 larger supply of nourishment than the Mouse; and relative 

 excess of nourishment makes possible a larger size without 

 a smaller rate of multiplication. How clearly this is the 

 cause, we see in the contrast between the common Eat and 

 the Water-Eat. While the common Eat has ordinarily 

 several broods a-year of from 10 to 12 each, the Water-Eat, 

 though somewhat smaller, has but 5 or 6 in a brood, and but 

 one brood, or sometimes two broods, a-year. But the Water- 

 Eat lives on vegetal food, and it lacks all that its bold, saga 

 cious, omnivorous congener gains from the warmth as well as 

 the abundance which men s habitations yield. 



The inverse variation of Individuation and Genesis is, 

 therefore, but approximate. Eecognizing the truth that 

 every increment of evolution which is appropriate to the 

 circumstances of an organism, brings an advantage somewhat 

 in excess of its cost; we see the general law, as more strictly 

 stated, to be that Genesis decreases not quite so fast as 

 Individuation increases. W T hether the greater Individuation 

 takes the form of a larger bulk and accompanying access of 

 strength; whether it be shown in higher speed or agility; 

 whether it consists in a modification of structure which facili 

 tates some habitual movement, or in a visceral change that 

 helps to utilize better the absorbed aliment; the ultimate 

 effect is identical. There is either a more economical per 

 formance of the same actions, internal or external, or there 

 is a securing of greater advantages by modified actions, which 



