118 ON THE INTERCROSSING [Chap. IT. 



any 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 understand 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 indi- 

 viduals which presented slight deviations of structure 

 mutually favourable 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 Ly ell's noble views on " the modern changes of 

 the earth, as illustrative of geology ; 5: but we now seldom 

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

 as trifling or insignificant, when used in explaining the 

 excavation of the deepest valleys or the formation of long 

 lines of inland cliffs. Xatural selection acts only by the 

 preservation and accumulation of small inherited modifi- 

 cations, each profitable to the preserved being ; and as 

 modern geology has almost banished such views as the 

 excavation of a great valley by a single diluvial wave, 

 so will natural selection banish the belief of the continued 

 creation of new organic beings, or of any great and sudden 

 modification in their structure. 



On the Intercrossing of Individuals. 



I must here introduce a short digression. In the case 

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

 obvious 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 



