OF NATURAL SBLnCTION. 89 



country, it might be a great advantage to the plant to have 

 a shorter or more deeply divided corolla, so that the hive- 

 bees should be enabled to suck its flowers. Thus I can un- 

 derstand how a flower and a bee might slowly become, 

 either simultaneously or one after the other, modified and 

 adapted to each other in the most perfect manner, by 

 the continued preservation of all the individuals which 

 presented slight deviations of structure mutually favorable 

 to each other. 



I am well aware that this doctrine of natural selection, 

 exemplified in the above imaginary instances, is open to 

 the same objections which were first urged against Sir 

 Charles Lyell's noble views on " the modern clianges of 

 the earth, as illustrative of geology;" but we now seldom 

 hear the agencies which we see still at work, spoken of as 

 trifling or insignificant, when used in explaining the excava- 

 tion of the deepest valleys or the formation of long lines of 

 inland cliffs. Natural selection acts only by the preserva- 

 tion and accumulation of small inherited modifications, 

 each profitable to the preserved being; and as modern geol- 

 ogy has almost banished such views as the excavation of a 

 great valley by a single diluvial wave, so will natural selec- 

 tion banish the belief of the continued creation of new or- 

 ganic beings, or of any great and sudden modification in 

 their structure. 



OIT THE IKTEECEOSSING OF INDIVIDUALS. 



I must here introduce a short digression. In the case of 

 animals and plants with separated sexes, it is of course ob- 

 vious that two individuals must always (with the ex- 

 ception of the curious and not well understood cases of 

 parthenogenesis) unite for each birth; but in the case of 

 hermaphrodites this is far from obvious. Nevertheless 

 there is reason to believe that with all hermaphrodites two 

 individuals, either occasionally or habitually, concur for 

 the reproduction of their kind. This view was long ago 

 doubtfully suggested by Sprengel Knight and Kolreuter. 

 We shall presently see its importance; but I must here 

 treat the subject with extreme brevity, though I have the 

 materials prepared for an ample discussion. All vertebrate 

 animals, all insects and some other large groups of animals. 



