174 ON THE ORIGIN OF SPECIES 



its loss through disuse or natural selection. But if the 

 electric organs had been inherited from one ancient 

 progenitor thus provided, we might have expected that 

 all electric fishes would have been specially related to 

 each other. Nor does geology at all lead to the belief 

 that formerly most fishes had electric organs, which 

 most of their modified descendants have lost. The 

 presence of luminous organs in a few insects, belong- 

 ing to different families and orders, offers a parallel 

 case of difficulty. Other cases could be given ; for 

 instance in plants, the very curious contrivance of a 

 mass of pollen-grains, borne on a foot-stalk with a 

 sticky gland at the end, is the same in Orchis and 

 Asclepias, — genera almost as remote as possible amongst 

 flowering plants. In all these cases of two very distinct 

 species furnished with apparently the same anomalous 

 organ, it should be observed that, although the general 

 appearance and function of the organ may be the same, 

 yet some fundamental difference can generally be de- 

 tected. I am inclined to believe that in nearly the 

 same way as two men have sometimes independently 

 hit on the very same invention, so natural selection, 

 working for the good of each being and taking advan- 

 tage of analogous variatious, has sometimes modified 

 in very nearly the same manner two parts in two 

 organic beings, which beings owe but little of their 

 structure in common to inheritance from the same 

 ancestor. 



Although in many cases it is most difficult to con- 

 jecture by what transitions organs could have arrived 

 at their present state ; yet, considering that the pro- 

 portion of living and known forms to the extinct and 

 unknown is very small, I have been astonished how 

 rarely an organ can be named, towards which no tran- 

 sitional grade is known to lead. The truth of this 

 remark is indeed shown by that old but somewhat 

 exaggerated canon in natural history of e 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 



