v.] IN THE THEORY OF NATURAL SELECTION. 313 



theory of natural selection. He says, for instance, in speaking 

 of the mutual adaptation observable between the proboscis, the 

 so-called 'tongue' of butterflies, and flowers with tubular 

 corolla^ :—' Among the most remarkable and commonest 

 adaptations observable in the forms of flowers, are the corollas 

 with long tubes considered in relation to the long "tongues" 

 of insects, which suck the nectar from the bottom of the long 

 narrow tubes, and at the same time effect the cross-fertilization 

 of the plant. Both these arrangements have been gradually 

 developed to their present degree of complexity — the long- 

 tubed corollas from those without tubes, and from those with 

 short ones, the long "tongues " from short ones. Undoubtedly 

 both have been developed at the same rate so that the length of 

 both sets of structures has always remained the same.' 



No objection can be raised against these statements, but 

 Nageli goes on to say : — ' But how can such a process of 

 development be explained by the theory of natural selection, 

 for at each stage in the process the adaptation was invariably 

 complete? The tube of the corolla and the "tongue" must 

 have reached, for instance, at a certain time, a length of 5 or 

 10 mm. If now the tube of the corolla became longer in some 

 plants, such an alteration would have been disadvantageous 

 because the insects would be no longer able to obtain food from 

 them, and would therefore visit flowers with shorter tubes. 

 Hence, according to the theory of natural selection, the longer 

 tubes ought to have disappeared. If on the other hand the 

 "tongue " became longer in some insects, such a change would 

 be superfluous and should have been given up, according to 

 the same theory, as unnecessar}'- structural waste. The simul- 

 taneous change in the two structures must, according to the 

 theory of natural selection, be due to the same principle as that 

 by which Miinchhausen pulled himself out of a bog by means 

 of his own pig-tail.' 



But, according to the theory of natural selection, the case 

 appears in a very different light from that in which it is put by 

 Nageh. The flower and the insect do not compete for the 

 greater length of their respective organs : all through the 

 gradual process, the flower is the first to lengthen its corolla and 

 the butterfly follows. Their relation is not like that between a 



1 1. c, p. 150. 



