160 MISCELLANEOUS OBJECTIONS TO THE [CHAP. VIL 



which before the principle of selection by man was well under- 

 stood, excited so much surprise in the minds of the older naturalists, 

 can thus be explained. 



It may be worth while to illustrate some of the foregoing remarks. 

 With respect to the assumed inutility of various parts and organs, 

 it is hardly necessary to observe that even in the higher and best- 

 known animals many structures exist, which are so highly deve- 

 loped that no one doubts that they are of importance, yet their 

 use has not been, or has only recently been, ascertained. As Bronn 

 gives the length of the ears and tail in the several species of mice 

 as instances, though trifling ones, of differences in structure which 

 can be of no special use, I may mention that, according to Dr. 

 Schiibl, the external ears of the common mouse are supplied in 

 an extraordinary manner with nerves, so that they no doubt serve 

 as tactile organs ; hence the length of the ears can hardly be quite 

 unimportant. We shall, also, presently see that the tail is a 

 highly useful prehensile organ to some of the species; and its 

 use would be much influenced by its length. 



With respect to plants, to which on account of Xageli's essay I 

 shall confine myself in the following remarks, it will be admitted 

 thrt the flowers of orchids present a multitude of curious structures, 

 which a few years ago would have been considered as mere morpho- 

 logical differences without any special function ; but they are now 

 known to be of the highest importance for the fertilisation of the 

 species through the aid of insects, and have probably been gained 

 through natural selection. No one until lately would have 

 imagined that in dimorphic and trimorphic plants the different 

 lengths of the stamens and pistils, and their arrangement, could 

 have been of any service, but now we know this to be the case. 



In certain whole groups of plants the ovules stand erect, and in 

 others they are suspended ; and within the same ovarium of some 

 few plants, one ovule holds the former and a second ovule the 

 latter position. These positions seem at first purely morphological, 

 or of no physiological signification ; but Dr. Hooker informs me that 

 within the same ovarium, the upper ovules alone in some cases, and 

 in other cases the lower ones alone are fertilised ; and he suggests 

 that this probably depends on the direction in which the pollen- 

 tubes enter the ovarium. If so, the position of the ovules, even 

 when one is erect and the other suspended within the same 

 ovarium, would follow from the selection of any slight deviations 

 in position which favoured their fertilisation, and the production 

 of seed. 



Several plants belonging to distinct orders habitually produce 

 flowers of two kinds, the one open of the ordinary structure, the 

 other closed and imperfect. These two kinds of flowers sometimes 

 differ wonderfully in structure, yet may be seen to graduate into 



