364 Darwin, and after Darwin. 
will subsequently endeavour to prove, there is abun- 
dant evidence to show that incipient characters are 
often developed to a large extent by causes other 
than natural selection (or apart from any reference to 
utility), with the result that some of them thus happen 
to become of use, when, of course, the supposed diffi- 
culty is at an end. 
But although it is thus easy to dispose of both the 
propositions in question, on account of their univer- 
sality, stated more carefully they would require, as 
I have said, more careful consideration. Thus, if it 
had been said that some incipient organs are presum- 
ably useless at the time of their inception, and that in 
some of these cases it is difficult, or impossible, to con- 
ceive how the principle of correlation, or any other 
principle hitherto suggested, can apply—then the 
question would have been raised from the sphere of 
logical discussion to that of biological fact. And 
the new question thus raised would have to be de- 
bated, no longer on the ground of general or abstract 
principles, but on that of special or concrete cases. 
Now until within the last year or two it has not been 
easy to find such a special or concrete case—that is to 
say, a case which can be pointed to as apparently 
excluding the possibility of natural selection having 
had anything to do with the genesis of an unquestion- 
ably adaptive structure. But eventually such a case 
has arisen, and the Duke of Argyll has not been slow 
in perceiving its importance. This case is the electric 
organ in the tail of the skate. No sooner had Pro- 
fessor Cossar Ewart published an abstract of his first 
paper on this subject, than the Duke seized upon it as 
a case for which, as he said, he had long been waiting 
