Chap. VI. TRANSITIONS OF ORGANS. 193 



their intimate structure closely resembles that of common 

 muscle ; and as it has lately been shown that Rays have 

 an organ closely analogous to the electric apparatus, and 

 yet do not, as Matteuchi asserts, discharge any electri- 

 city, we must own that we are far too ignorant to argue 

 that no transition of any kind is possible. 



The electric organs offer another and even more 

 serious difficulty ; for they occur in only about a dozen 

 fishes, of which several are widely remote in their 

 affinities. Generally when the same organ appears in 

 several members of the same class, especially if in 

 members having very different habits of life, we may 

 attribute its presence to inheritance from a common 

 ancestor ; and its absence in some of the members to 

 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 in- 

 stance 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 spe- 

 cies 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 



K 



