98 INTEECEOSSING OF INDIVIDUALS. Chap. IV. 



tlio llowiTri, if humble-bees were to become rare in any country, 

 it miglit be a great advantage to the plant to have a shorter 

 or more deeply-divided corolhi, so that the hive-bees should be 

 induced 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 M'hich presented slight deviations of structure 

 mutually favorable to each other. 



I am Avcll aware that this doctrine of natural selection, 

 exemplified in the above imaginary instances, is open to the 

 same objections which were at first urged against Sir Charles 

 Lycll's noble \aews on " the modern changes of the earth, as 

 illustrative of geology ; " but Ave now seldom hear the agencies, 

 still at work, spoken of as trifling or insignificant, when applied 

 to the excavation of the deepest valleys or to the formation of 

 long lines of inland cliffs. Natural selection acts only by the 

 preservation and accumulation of small inherited modifications, 

 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, if 

 it be a true principle, banish the belief of the continued crea- 

 tion of new organic beings, or of any great and sudden modifi- 

 cation in their structure. 



On the Infererossmff 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 parthenogenesis) 

 unite for each birth ; but in the case of hermaphrodites this is 

 far from obvious. Nevertheless tliere is reason to believe that 

 with all hermaphrodites two individuals, either occasionally or 

 habitually, concur for the reproduction of their kind. This 

 vicAV was first suggested by Andrew Knight. "SVe shall pres- 

 enth' see its importance : but I must here treat the subject 

 with extreme 1)revity, thougli I have the materials prepared 

 for an anijile discussion. All vertebrate animals, all insects, 

 and some other large groups of animals, pair for each birth. 

 Modern research has nuich diminished the number of supjiosed 

 hermajihrodites, and of real hermaphrodites a large number 

 pair; that is, two individuals regularly unite for reproduction, 



