ON THE INTERCROSSING OF INDIVIDUALS 109 



bees were to become rare in any country, it might be a great 

 advantage to the plant to have a shorter or more deeply di- 

 vided 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 individuals 

 which presented slight deviations of structure mutually fa- 

 vourable 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 changes 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 insignifi- 

 cant, when used in explaining the excavation of the deepest 

 valleys or the formation of long lines of inland cliffs. Nat- 

 ural selection acts only by the preservation and accumulation 

 of small inherited modifications, each profitable to the pre- 

 served 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 obvi- 

 ous that two individuals must always (with the exception of 

 the curious and not well understood cases of parthenogene- 

 sis) unite for each birth; but in the case of hermaphrodites 

 this is far from obvious. Nevertheless there is reason to be- 

 lieve 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 Kolreutcr. We shall presently sec 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 



