202 MISCELLANEOUS OBJECTIONS TO THE 



appear to be of no service whatever to their possessors, and 

 therefore cannot have been influenced through natural 

 selection. Bronn adduces the length of the ears and tails 

 in the different species of hares and mice — the complex 

 folds of enamel in the teeth of many animals, and a multi- 

 tude of analogous cases. With respect to plants, this sub- 

 ject has been discussed by Nageli in an admirable essay. 

 He admits that natural selection has effected much, but he 

 insists that the families of plants differ chiefly from each 

 other in morphological characters, which aj^pear to be quite 

 nnimportant for the welfare of the species. He conse- 

 quently believes in an innate tendency toward progressive 

 and more perfect development. He specifies the arrange- 

 ment of the cells in the tissues, and of the leaves on the 

 axis, as cases in which natural selection could not have 

 acted. To these may be added the numerical divisions in 

 the parts of the flower, the position of the ovules, the 

 shape of the seed, when not of any use for dissemina- 

 tion, etc. 



There is much force in the above objection. Neverthe- 

 less, we ought, in the first place, to be extremely cautious 

 in pretending to decide what structures now are, or have 

 formerly been, of use to each species. In the second place, 

 it should always be borne in mind that when one part is 

 modified, so will be other parts, through certain dimly seen 

 causes, such as an increased or diminished flow of nutri- 

 ment to a part, mutual pressure, an early developed part 

 affecting one subsequently developed, and so forth — as well 

 as through other causes which lead to the many mysterious 

 cases of correlation, which we do not in the least under- 

 stand. These agencies may be all grouped together, 

 for the sake of brevity, under the expression of 

 the laws of growth. In the third place, we have 

 to allow for the direct and definite action of 

 changed conditions of life, and for so-called spontaneous 

 variations, in which the nature of the conditions appar- 

 ently plays a quite subordinate part. Bud-variations, such 

 as the appearance of a moss-rose on a common rose, or of 

 a nectarine on a peach-tree, offer good instances of spon- 

 taneous variations; but even in these cases, if we bear in 

 mind the power of a minute drop of poison in producing 

 complex galls, we ought not to feel too sure that the above 



