234 DIFFICULTIES OF THE THEOEY [Chap. TI 



Special Difficulties of the Theory of Natural Selection. 



Although we must be extremely cautious in con- 

 eluding that any organ could not have been produced 

 by successive, small, transitional gradations, yet un- 

 doubtedly 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 Bay, 

 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 

 Bay, besides the organ just referred to, there is, as Dr. 

 B. 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 ordinary muscle a close analogy, in intimate 

 structure, in the distribution 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. RadclifTe 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 



