236 DIFFICULTIES OF THE THEOKY [Chap. VI. 



from different sources, and this is perhaps the most 

 important of all the differences. Hence in the several 

 fishes furnished with electric organs, these cannot be 

 considered as homologous, but only as analogous in 

 function. Consequently there is no reason to suppose 

 that they have been inherited from a common pro- 

 genitor ; for had this been the case they would have 

 elosely resembled each other in all respects. Thus the 

 difficulty of an organ, apparently the same, arising in 

 several remotely allied species, disappears, leaving only 

 the lesser yet still great difficulty ; namely, by what 

 graduated steps these organs have been developed in 

 each separate group of fishes. 



The luminous organs which occur in a few insects, 

 belonging to widely different families, and which are 

 situated in different parts of the body, offer, under our 

 present state of ignorance, a difficulty almost exactly 

 parallel with that of the electric organs. Other similar 

 cases could be given ; for instance in plants, the very 

 curious contrivance of a mass of pollen-grains, borne on 

 a foot-stalk with an adhesive gland, is apparently the 

 same in Orchis and Asclepias, — genera almost as 

 remote as is possible amongst flowering plants; but 

 here again the parts are not homologous. In all cases 

 of beings, far removed from each other in the scale of 

 organisation, which are furnished with similar and 

 peculiar organs, it will be found that although the 

 general appearance and function of the organs may be 

 the same, yet fundamental differences between them 

 can always be detected. For instance, the eyes of 

 cephalopods or cuttle-fish and of vertebrate animals 

 appear wonderfully alike ; and in such widely sun- 

 dered groups no part of this resemblance can be due 



