266 MISCELLANEOUS OBJECTIONS TO THE [Chap. VIL 



sessors, 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 multitude of analogous cases. With 

 respect to plants, this subject has been discussed by 

 Nageli in an admirable essay. He admits that natural 

 selection has eilected much, but he insists that the 

 families of plants differ chiefly from each other in mor- 

 phological characters, which appear to be quite unim- 

 portant for the welfare of the species. He. consequently 

 believes in an innate tendency towards progressive 

 and more perfect development. He specifies the ar- 

 rangement of the cells in the tissues, and of the leaves 

 on the axis, as eases in which natural selection could not 

 have acted. To these may be added the numerical divi- 

 sions in the parts of the flower, the position of the ovules, 

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

 tion, &c. 



There is much force in the above objection. Never- 

 theless, 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 nutriment to a part, mutual pres- 

 sure, 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 understand. These agen- 

 cies may be all grouped together, for the sake of brevity, 

 under the expression of the laws of growth. In the 



