370 PHYSIOLOGICAL DEVELOPMENT. 



phenomena so multitudinous and varied, it has been imprs 

 ticable to deal with any but the most important; and it has 

 been practicable to deal with these only in a general way. 

 Much, however, as remains to be explained, I think the possi- 

 bility of tracing, in so many cases, the actions to which these 

 internal differentiations may rationally be ascribed, makes it 

 likely that the remaining internal differentiations are due to 

 kindred actions. We find evidence that, in more cases 

 than seemed probable, these actions produce their effects 

 directly on the individual; and that the unlikenesses are 

 produced by accumulation of such effects from generation to 

 generation. While for all the other unlikenesses, we have, 

 as an adequate cause, the indirect effects wrought by the sur- 

 vival, generation after generation, of the individuals in which 

 favourable variations have occurred — variations such as those 

 of which human anatomy furnishes endless instances. Thus 

 accounting for so much, we may not unreasonably presume 

 that these co-operative processes of direct and indirect equili- 

 bration will account for what remains. 



[Note. — After having dismissed this revised chapter as 

 done with, and sent it to the printer, further thought con- 

 cerning those differentiations which produce bone, has re- 

 minded me of a fact of extreme and varied significance 

 named in the first volume. I refer to the formation of 

 adaptive structures round the ends of dislocated bones, and 

 to the formation of " false joints." 



These are ontogenetic changes of which phylogeny yields 

 no explanation. They do not repeat the traits of ancestral 

 organisms, and they cannot be ascribed to either of the 

 recognized evolutionary factors. If a humerus be broken 

 across and, failing to set, presently comes to have its two 

 loose ends so modified as in a measure to simulate the parts 

 of a normal joint — the ends becoming smooth, covered with 

 periosteum and supplied with fibrous tissue, and attached 

 by ligaments in such ways as to allow of restrained move- 



