434 J^AWS OF MULTIPLICATION. 



in the inner actions required to counter-balance them. Even 

 were species similarly conditioned, self-preservation would 

 require of them extremely unlike expenditures of force. 



The cost of locomotion increases in a greater ratio than 

 the size. In virtue of the law that the weights of animals in- 

 crease as the cubes of their dimensions, while their powers of 

 bearing strains increase only as the squares of their dimen- 

 sions (§46), preservation of its various attitudes requires a 

 large animal to consume more substance in proportion to its 

 weight, than it requires a small animal to consume ; and there 

 results, other things equal, a difficulty of self-maintenance 

 which augments in a more rapid ratio than the bulk. Nor 

 must we overlook the further complication, that among 

 aquatic creatures the variation of resistance of the medium 

 tends to produce an opposite effect. 



Again, the heat-consumption is a changing element in the 

 total expense of self-preservation. Creatures which have tem- 

 peratures scarcely above that of the air or water, may, other 

 things equal, accumulate more surplus nutriment than crea- 

 tures which have to keep their bodies warm spite of the con- 

 tinual loss by radiation and conduction. This difference of 

 cost is modified by the presence or absence of natural cloth- 

 ing; and it is also modified by unlikenesses of size. Here 

 the bulky animals have the advantage : small masses cooling 

 more rapidly than large ones. 



Dissimilarities of attack and defence are also causes of 

 variation in the outlay for self-maintenance. A creature that 

 has to hunt, as compared with another that gets a sufficiency 

 of prey by lying in wait, or a creature that escapes by speed 

 as compared with another that escapes by concealment, 

 obviously leads a life that is physiologically more costly. 

 Animals which protect themselves passively, as the Hedge-hog 

 by its spines or as the Skunk and the Musk-rat by their in- 

 tolerable odours, are relatively economical; and have the 

 more vital capital for other purposes. 



Amplification is needless. These instances will show that 



