260 THE ORIGIN OF SPECIES 



often or ever been modified through this comparatively 

 sudden mode of transition 1 can form no opinion; but 

 if this has occurred, it is probable that the differences 

 between the young and the mature, and between the 

 mature and the old, were primordially acquired by 

 graduated steps. 



Special Difficulties of the Theory of Natural Selection 



Although we must be extremely cautious in conclud- 

 ing that any organ could not have been produced by 

 successive, small, transitional gradations, yet undoubtedly 

 serious cases of difficulty occur. 



One of the most serious is that of neuter insects, 

 which are often differently constructed from either the 

 males or fertile females; but this case will be treated of 

 in the next chapter. The electric organs of fishes offer 

 another case of special difficulty; for it is impossible to 

 conceive by what steps these wondrous organs have been 

 produced. But this is not surprising, for we do not even 

 know of what use they are. In the Gymnotus and Tor- 

 pedo they no doubt serve as powerful means of defence, 

 and perhaps for securing prey; yet in the Kay, as ob- 

 served by Matteucci, an analogous organ in the tail mani- 

 fests but little electricity, even when the animal is greatly 

 irritated; so little, that it can hardly be of any use for 

 the above purposes. Moreover, in the Ray, besides the 

 organ just referred to, there is, as Dr. R. M'Donnell has 

 shown, another organ near the head, not known to be 

 electrical, but which appears to be the real homologue 

 of the electric battery in the Torpedo. It is generally 

 admitted that there exists between these organs and ordi- 

 nary muscle a close analogy, in intimate structure, in the 



