168 DIFFICULTIES OF THE THEORY 



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 referred to, there is, as Dr. R. McDon- 

 nell 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. 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 peculiar, may be only another form 

 of the discharge which attends upon 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 fishes, it would be extremely bold to maintain that 

 no serviceable transitions are possible by which these organs 

 might have been gradually developed. 



These organs appear at first to offer another and far more 

 serious difficulty ; for they occur in about a dozen kinds of 

 fish, of which several are widely remote in their affinities. 

 When the same organ is found in several members of the 

 same class, especially if in members having very different 

 habits of life, we may generally attribute its presence t« 

 inheritance from a common ancestor ; and its absence in 

 some of the members to loss through disuse or natural selec- 

 tion. So that, if the electric organs had been inherited from 

 some one ancient progenitor, we might have expected that 

 all electric fishes would have been specially related to each 

 other ; but this is far from the case. Nor does geology at 

 all lead to tfhe belief that most fishes formerly possessed 



