32 THE GEXESIS OF SPECIES. [Ch>p. 



lure ; and in ])rodiicing, as well as in arresting, every one 

 of its movements, it has to overcome eight times the 

 inertia. ^Fean while, the muscles and l)ones have severally 

 increased their contractile and resisting powers, in propor- 

 tion to the areas of their transverse sections ; and hence 

 are severally hut four times as strong as they were. Thus, 

 while the creature has doul)led in height, and while its 

 ability to overcome forces has quadrupled, the forces it has 

 to overcome have ^rown ei^ht times as jrreat. Hence, to 

 raise its body through a given space, its muscles have to 

 be contracted with twice the intensitv, at a double cost of 

 matter expended." Again, as to the cost at which nutri- 

 ment is distributed through the body, and effete matters 

 removed from it, " Each increment of growth being added 

 at the periphery of an organism, the force expended in the 

 transfer of matter mnst increase in a rapid progression — 

 a prngi'ession more rapid than that of the mass." 



There is yet another point. Vast as may have been flie 

 time during which the process of evolution has continued, 

 it is nevertheless not infinite. Yet, as eA^ery kind, on the 

 Darwinian hyjiothesis, varies slightly but indefinitely in 

 evei'y organ and every part of every organ, how very 

 generally must favmirable variations as to the length of 

 the neck have been accompanied by some unfavourable 

 variation in some other part, neutralizing the actimi of 

 the favouralde one, the latter, moreover, only taking 

 effect during these periods of drought! How often must 

 individuals, favoured by a slightly increased length of 

 n-eck, have failed to enjoy the elevated foliage which they 

 had not strength or endurance to attain ; while other indi- 

 viduals, exceptionally robust, could ictruggle on yet further 

 till the-v arrived at vegetation witliin their reach. 



