58 ORIGINAL ARTICLES. 



On the other hand, the candid inquirer must admit, that when in 

 some creatures well-developed special organs exist, while in their im- 

 mediate kinsfolk (if I may use the term) no trace of kindred structures 

 has been discovered, there herein exists a grave objection to any theory 

 of unity of type resulting from community of descent. This difficulty 

 appears to have been more obvious to Mr. Darwin than to most of the 

 reviewers who have undertaken to criticize his views, or at least has 

 been more clearly and fairly stated by the former than by the latter ; 

 and he speaks of the case of the electrical organs of fishes as one of spe- 

 cial difficulty. 



The presence of modified, atrophied, or rudimentary organs, consti- 

 tutes one of the strongest arguments in favour of Mr. Darwin's theory ; 

 for the supposition is as unsatisfactory as it is improbable, that such 

 organs are the result of what would seem a whimsical exercise of cre- 

 ative power in framing an organ merely for the sake of symmetry. The 

 total absence, however, of any trace of even an altered or rudimentary 

 organ representing a structure known to exist in certain members of a 

 group, would afford good testimony against the theory of descent ; as it 

 would be at least in the highest degree improbable that such a structure 

 should not have its homological representative existing in some form in 

 the immediate members of the same family. 



Considering, therefore, that on the theory of Mr. Darwin it was in 

 the highest degree improbable that the electric organs of the Torpedo 

 were totally absent in the Skates, I undertook a careful search, with 

 the view of following out their homologies; determining to do so by trac- 

 ing the nerves corresponding with those which go to supply the bat- 

 teries of the Torpedo. I have thus been led to make out the bodies 

 which I conceive to be the true homologues of the Torpedo's wondrous 

 organs ; and the anatomical position and peculiarities of which I shall 

 briefly point out. If the skin be removed from the fore part of the 

 back of a common Skate, the following parts will be readily found, a 

 short distance behind the temporal orifice : — 1st. That band of the so- 

 called muciferous tubes which runs inwards and a little backwards from 

 a point external and anterior to the gills ; 2nd. The dorsal aspect of the 

 branchial chambers ; and, 3rd. The little snout-muscle, which ends in 

 a long delicate tendon, running forwards. Let the little fleshy belly of 

 the snout-muscle be raised and drawn outwards, and the band of tubes 

 dissected up and drawn forwards, in the angle between them will be 

 found the body sought for ; it will not, however, be very apparent to 

 the naked eye ; but if brushed over with some tolerably strong acetic 

 acid, it will become quite distinctly visible. It will be found to be 

 more than an inch long in an ordinary sized fish, wedged in between the 

 occipital muscles internally and the gills externally, covered super- 

 ficially by the snout-muscle and tubes already mentioned, and dipping 

 down so as to reach the branches of the vagus going to the branchial 

 arches. Its upper surface is triangular, the apex behind the base in 

 front, in contact with one of the large jaw muscles. When made evi- 

 dent by the aid of acetic acid, this little body is seen to consist of a 



