THE FACTORS OP ORGANIC EVOLUTION. 15 



the increased massiveness of the lower part of tlie neck ; 

 the increased size and strength of the thorax required to 

 bear the additional burden ; and the increased strength 

 of the fore-legs required to carry the greater weight of 

 both. But now I think that further consideration suggests 

 the belief that the entailed modifications are much more 

 numerous and remote than at first appears; and that the 

 greater part of these are such as cannot be ascribed in any 

 rdegree to the selection of favourable variations, but must 

 / be ascribed exclusively to the inherited effects of changed 

 v functions. Whoever has seen a giraffe gallop will long 

 remember the sight as a ludicrous one. The reason for the 

 strangeness of the motions is obvious. Though the fore 

 limbs and the hind limbs differ so much in length, yet in 

 galloping they have to keep pace must take equal strides. 

 The result is that at each stride, the angle which the hind 

 limbs describe round their centre of motion is much larger 

 than the angle described by the fore limbs. And beyond 

 this, as an aid in equalizing the strides, the hind part of 

 the back is at each stride bent very much downwards and 

 forwards. Hence the hind-quarters appear to be doing 

 nearly all the work. Now a moment s observation shows that 

 the bones and muscles composing the hind-quarters of the 

 giraffe, perform actions differing in one or other way and 

 degree, from the actions performed by the homologous 

 bones and muscles in a mammal of ordinary proportions, 

 and from those in the ancestral mammal which gave origin 

 to the giraffe. Each further stage of that growth which 

 produced the large fore-quarters and neck, entailed some 

 adapted change in sundry of the numerous parts composing 

 the hind-quarters; since any failure in the adjustment of 

 their respective strengths would entail some defect in speed 

 and consequent loss of life when chased. It needs but to 

 remember how, when continuing to walk with a blistered 

 foot, the taking of steps in such a modified way as to 

 diminish pressure on the sore point, soon produces aching 



