ADAPTATION 349 



producing so elaborate an organ did not entail the sacrifice 

 of efficiency in other directions (e.g. in egg-production) . 



Specialisation. — A somewhat different use of the term 

 adaptation involves the notion of specialisation. This usage 

 may be simply illustrated from amongst the solitary bees. 

 Many species of these visit a wide range of flowers ; whereas 

 others obtain their pollen and nectar from one or two species 

 only. Robertson especially, in America, has recorded the 

 habits of many ' oligolectic ' bees. It is often claimed that 

 the bee species whose choice is so restricted are highly adapted, 

 and the phenological data, proving an exceedingly close 

 correspondence between the flowering-time and the active 



A. B. C. 



Fig. 29. — Oligolectic and Polytrophic Bees. 



A. Macropis labiata F., obtains its pollen only from Lysimachia vulgaris. 



B. Bomb us lapponicus F., restricted to regions where Vaccinium spp. flourish, 



but visits other flowers early in the year, before Vaccinium is in bloom. 



C. B. pratorum L., closely allied to B. lapponicus but visits numerous flowers. 



Photos, W. H. T. Tarns. 



period of the adult bee, are cited in favour of this view. It 

 is important to note that there is normally little evidence of 

 much structural modification of the bees to suit their par- 

 ticular flower. In a general way flowers with long corollas 

 and deeply sunk nectaries are visited by long-tongued bees, 

 and vice versa, but the correlation is not very high, and many 

 oligolectic bees which visit different flowers do not appear 

 to be specially suited to their chosen source of food. It is 

 usual to treat such examples of specialisation as adaptations 

 in the restricted sense, but there is little logical justification 

 for so doing. The bees exist, therefore we may say they are 

 sufficiently adapted to survive, but this in itself throws no 

 light on the survival value of particular habits or structures. 

 It is interesting to examine Darwin's views on this point. In 

 chapter iv of ' The Origin of Species ' he examines the problem 



