Chap. IV. VAEIOUS OBJECTIONS. 12^ 



ill single cliaractcrs, ])ut in man}- parts; and he asks, how it 

 comes that natural selection should invariably have afrectcd 

 simultaneously many parts of the org'anization i' But there is 

 not the loast necessity for believing that all the parts have been 

 simultaneously modilied ; they may have been gained one after 

 the other, and from being transmitted together, they appeal 

 to us as if simultaneously formed. Correlation, however, will 

 account for various parts changing, when any one part changes. 

 We have e\'idence of this in our domestic races, which, though 

 they may difl'er greatly in some one selected character, always 

 diller to a certain extent in other characters. 



Bronn, again, asks how natural selection can account for 

 dilTerences between species, which appear to be of no service 

 to these species, such as the length of the ears or tail, or the 

 folds of the enamel in the teeth, of the several species of hares 

 and mire ? With respect to plants, this subject has been 

 recently discussed by Niigeli in an admirable essay. He admits 

 that natural selection has effected much, but he urges that the 

 families of plants diil'er chiefly from each other in morphologi- 

 cal characters, which seem quite imimportant for the welfare 

 of the species. He consequently believes in an innate ten- 

 dency toward perfection or progressive development. He 

 specifies the arrangement of the cells in the tissues, and of the 

 leaves on the axis, as cases in which natural selection Avould 

 fail to act. To these may be added the numerical divisions 

 in the parts of the flower, the position of the ovniles, the shape 

 of the seed, when not of any use for dissemination, etc Prof. 

 Weismann, in discussing Niigeli's essay, accounts for such dif- 

 f(!rences by the nature of the varying organism under the action 

 of certain conditions ; and this is the same with what I have 

 called the direct and definite action of the conditions of lifo, 

 causing all or nearly all the individuals of the same species to 

 vary in the same manner. When we remember such cases as 

 the formation of the more complex galls, and certain monstros- 

 ities, which cannot be accounted for l)y reversion, cohesion, 

 etc., and sudden strongly-marked deviations of structure, such 

 as the ajipearance of a moss-roscj on a connnon rose, we must 

 admit that the organization of the individual is capable through 

 its own laws of growth, under certain conditions, of undergoing 

 great modifications, independently of the gradual accumulation 

 of slight inherited modifications. \'arious morphological differ- 

 ences probably come under this head, to which we sliall recur; 

 but many differences may at the present time be of high ser- 



