INADEQUACY OP NATURAL SELECTION, ETC. 619 



their phalanges. Stronger muscles and tendons imply greater 

 strains on the joints ; and unless these are strengthened, one or 

 other, dislocation will be caused by a more vigorous spring. Not 

 only the articulations themselves must be so modified as to bear 

 greater stress, but also the numerous ligaments which hold the 

 parts of each in place. Nor can the bodies of the bones remain 

 unstrengthened ; for if they have no more than the strengths 

 needed for previous movements they will fail to bear more violent 

 movements. Thus, saying nothing of the required changes in 

 the pelvis, as well as in the nerves and blood-vessels, there are, 

 counting bones, muscles, tendons, ligaments, at least fifty differ- 

 ent parts in each hind leg which have to be enlarged. More- 

 over they have to be enlarged in unlike degrees. The muscles 

 and tendons of the outer toes, for example, need not be added to 

 so much as those of the median toes. Now, throughout their 

 successive stages of growth, all these parts have to be kept fairly 

 well balanced ; as any one may infer on remembering sundry of 

 the accidents he has known. Among my own friends I could 

 name one who, when playing lawn-tennis, snapped the Achilles 

 tendon ; another who, while swinging his children, tore some of 

 the muscular fibres in the calf of his leg ; another who, in getting 

 over a fence, tore a ligament of one knee. Such facts, joined 

 with every one's experience of sprains, show that during the 

 extreme exertions to which limbs are now and then subject, there 

 is a giving way of parts not quite up to the required level of 

 strength. How, then, is this balance to be maintained ? Suppose 

 the extensor muscles have all varied appropriately ; their varia- 

 tions are useless unless the other co-operative parts have also varied 

 appropriately. Worse than this. Saying nothing of the dis- 

 advantage caused by extra weight and cost of nutrition, they will 

 be causes of mischief causes of derangement to the rest by con- 

 tracting with undue force. And then, how long will it take for 

 the rest to be brought into adjustment ? As Mr. Darwin says 

 concerning domestic animals : " Any particular variation would 

 generally be lost by crossing, reversion, &c. . . . unless care- 

 fully preserved by man." In a state of nature, then, favourable 

 variations of these muscles would disappear again long before one 

 or a few of the co-operative parts could be appropriately varied, 

 much more before all of them could. 



With this insurmountable difficulty goes a difficulty still more 

 insurmountable if the expression may be allowed. It is not a 

 question of increased sizes of parts only, but of altered shapes of 

 parts, too. A glance at the skeletons of mammals shows how 

 unlike are the forms of the corresponding bones of their limbs ; 

 and shows that they have been severally re-moulded in each 

 species to the different requirements entailed by its different 



