Chap. VII.] THEOEY OF NATUEAL SELECTION. 273 



We thus see that with plants many morphological 

 changes may be attributed to the laws of growth and 

 the inter-action of parts, independently of natural selec- 

 tion. Bat with respect to Nageli's doctrine of an innate 

 tendency towards perfection or progressive development, 

 can it be said in the case of these strongly pronounced 

 variations, that the plants have been caught in the act 

 of progressing towards a higher state of development ? 

 On the contrary, I should infer from the mere fact of 

 the parts in question differing or varying greatly on the 

 same plant, that such modifications were of extremely 

 small importance to the plants themselves, of whatever 

 importance they may generally be to us for our classi- 

 fications. The acquisition of a useless part can hardly 

 be said to raise an organism in the natural scale ; and 

 in the case of the imperfect, closed flowers above des- 

 cribed, if any new principle has to be invoked, it must 

 be one of retrogression rather than of progression ; and 

 so it must be with many parasitic and degraded animals. 

 We are ignorant of the exciting cause of the above speci- 

 fied modifications ; but if the unknown cause were to act 

 almost uniformly for a length of time, we may infer that 

 the result would be almost uniform ; and in this case 

 all the individuals of the species would be modified in 

 the same manner. 



From the fact of the above characters being unimpor- 

 tant for the welfare of the species, any slight variations 

 which occurred in them would not have been accumu- 

 lated and augmented through natural selection. A 

 structure which has been developed through long-con- 

 tinued selection, when it ceases to be of service to a 

 species, generally becomes variable, as we see with rudi- 

 mentary organs ; for it will no longer be regulated by 



