236 DIFFICULTIES OF THE THEOEY [Chap. VL 



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 progeni- 

 tor; for had this been the case they would have closely 

 resembled each other in all respects. Thus the diffi- 

 culty of an organ, apparently the same, arising in several 

 remotely allied species, disappears, leaving only the 

 lesser yet still great difficulty; namely, by what gradu- 

 ated steps these organs have been developed in each sep- 

 arate 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 

 eases 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 re- 

 mote 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 or- 

 ganisation, which are furnished with similar and pe- 

 culiar organs, it will be found that although the gen- 

 eral appearance and function of the organs may be the 

 same, yet fundamental differences between them can 

 always be detected. For instance, the eyes of cephalo- 

 pods or cuttle-fish and of vertebrate animals appear won- 

 derfully alike; and in. such widely sundered groups 

 no part of this resemblance can be due to inheritance 



