DIFFICULTIES OF THE THEORY 153 



duction were retarded, the character of the species, at least in its 

 adult state, would be modified; nor is it improbable that the pre- 

 vious and earlier stages of development would in some cases be 

 hurried through and finally lost. Whether species have often or 

 ever been modified through this comparatively sudden mode of 

 transition, I 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 concluding that any 

 organ could not have been produced by successive, small, transi- 

 tional 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 torpedo they no doubt 

 serve as powerful means of defence, and perhaps for securing prey; 

 yet in the ray, as observed by Matteucci, an analogous organ in 

 the tail manifests 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 re- 

 ferred to, there is, as Dr. R. McDonnell 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 

 ordinary muscle a close analogy, in intimate structure, in the dis- 

 tribution of the nerves, and in the manner in which they are acted 

 on by various reagents. It should, also, be especially observed that 

 muscular contraction is accompanied by an electrical discharge; 

 and, as Dr. Radcliffe insists, "in the electrical apparatus of the 

 torpedo during rest, there would seem to be a charge in every 

 respect like that which is met with in muscle and nerve during the 

 rest, and the discharge of the torpedo, instead of being Deculiar, 

 may be only another form of the discharge which attendsTipon the 

 action of muscle and motor nerve." Beyond this we cannot at 

 present go in the way of explanation; but as we know so little 

 about the uses of these organs, and as we know nothing about the 

 habits and structure of the progenitors of the existing electric 



