OF NATVRAL SELECTION, 185 



antenna. ^ This antenna, when touched, transmits a sensa- 

 tion or vibration to a certain membrane which is instantly 

 ruptured; this sets free a spring by which tlie pollen- mass 

 is shot .^orth, 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 retain the pollen, thus effecting fertilization. 



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

 able other instances, can we understand the graduated 

 scale of complexity and the multifarious means for gaining 

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

 marked, 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 also bear 

 in mind that every highly developed organism has passed 

 through many changes; and that each modified structure 

 tends to be inherited, so that each modification will not 

 readily be quite lost, but may be again and again further 

 altered. Hence, the structure of each part of each species, 

 for whatever purpose it may serve, is the sum of many 

 inherited changes, through which the species has passed 

 during its successive adaptations to changed habits and 

 conditions of life. 



Finally then, although in many cases it is most difticult 

 even to conjecture by what transitions organs have ariivcd 

 at their present state; yet, considei'ing how small the pro- 

 portion of living and known forms is to the extinct and 

 unknown, I have been astonished how rarely an organ can 

 be named, toward which no transitional grade is known to 

 lead. It certainly is true, that new organs appearing as if 

 created for some special purpose rarely or never appear in 

 any being; as indeed is shown by that old, but somewhat 

 exaggerated, canon in natural history of " Natura non facit 

 saltum." We meet with this admission in the writings of 

 almost every experienced naturalist; or as Milne Edwards 

 has well expressed it, ^* Nature is prodigal in variety, but 

 niggard in innovation.'' Why, on the theory of Creation, 



