

DIFFICULTIES OF THE THEORY 269 



lertilized. Now at last we see the full use of every part 

 of the flower, of the water-secreting horns, of the bucket 

 half full of water, which prevents the bees from flying 

 away, and forces them to crawl out through the spout, 

 and rub against the properly placed viscid pollen-masses 

 and the viscid stigma. 



The construction of the flower in another closely allied 

 orchid, namely the Catasetum, is widely different, though 

 serving the same end; and is equally curious. Bees visit 

 these flowers, like those of the Coryanthes, in order to 

 gnaw the labellum; in doing this they inevitably touch a 

 long, tapering, sensitive projection, or, as I have called 

 it, the antenna. This antenna, when touched, transmits a 

 sensation or vibration to a certain membrane which is 

 instantly ruptured; this sets free a spring by which the 

 pollen-mass is shot forth, like an arrow, in the right 

 direction, and adheres by its viscid extremity to the 

 back of the bee. The pollen-mass of the male plant 

 (for the sexes are separate in this orchid) is thus carried 

 to the flower of the female plant, where it is brought 

 into contact with the stigma, which is viscid enough to 

 break certain elastic threads, and retaining the pollen, 

 fertilization is effected. 



How, it may be asked, in the foregoing and in innu- 

 merable other instances, can we understand the graduated 

 scale of complexity and the multifarious means for gain- 

 ing the same end. The answer no doubt is, as already 

 remarked, that when two forms vary, which already differ 

 from each other in some slight degree, the variability 

 will not be of the same exact nature, and consequently 

 the results obtained through natural selection for the 

 same general purpose will not be the same. We should 



