m'donnell on the electric organ of the skate. 59 



number of quadrangular and pentangular masses, of minute size and 

 rather irregular form, packed closely together like a mosaic work, ar- 

 ranged vertically, and somewhat resembling a small conglobate gland 

 in appearance. Examined microscopically, it is found to consist for the 

 most part of an abundant, soft, yellowish substance, composed of mi- 

 nute round granules, nearly all equal in point of size, and apparently 

 devoid of nuclei. This granular matter is entangled in an abundant 

 areolar texture, in which, when washed several times, there are to be 

 discovered peculiar nucleated bodies, large, and varying considerably in 

 dimensions, which are at first obscured by the granular matter, and 

 seem to be more or less intimately connected with the small nervous 

 ramifications. Neither when viewed by the naked eye, nor by the aid 

 of the microscope, does this organ in the least resemble the tail electric 

 organ discovered by Stark. Unless the peculiar nucleated bodies al- 

 ready mentioned (and which form indeed a very small part of the mass) 

 be regarded as a modified condition of it, nothing like the " tissue elec- 

 trique" of Robin exists in the body I have described, while the tail- 

 organ is almost entirely made up of this tissue (Kolliker's Schwamm- 

 Korper). 



The nerves supplying the little body which I have described are, 

 first, minute filaments derived from the branches of the vagus going to 

 the gills ; and, secondly, a larger one, derived from the posterior branch 

 of the fifth pair, which takes the following course : — If the large branch 

 of the fifth, which is found under the skin immediately behind the tem- 

 poral orifice, be followed backwards, it will be seen, that after escaping 

 from the cranial cartilage, it gives a branch backwards, which enters the 

 muscle behind it, and, supplying this muscle with several twigs, passes 

 through it to reach the body in question, which it supplies, also giving 

 a little twig to the snout-muscle which covers it. 



On carefully inspecting this large division of the fifth pair, the dif- 

 ference of colour is quite obvious between that portion which is destined 

 to go to the ampulla, from which the so-called muciferous tubes take rise, 

 and that portion destined for the muscles; nor is it uninteresting to 

 observe, that the branch going to the supposed homologue of the electric 

 organ is derived from the latter. I need not say that it would be quite 

 impossible to trace so minute a nerve so as to find out whether, at its 

 origin, it may be related to the anterior or posterior columns of the cord; 

 but the fact mentioned tends to support the view that it is related to 

 the motor tract. 



As the lateral line system exists in the torpedo and other electric 

 fish, in a rather remarkable condition of development, the opinion held 

 by some authors may be set aside, that it in other fishes represents the 

 electric organs ; the same may be said for the so-called muciferous sys- 

 tem of rays and sharks (which Geoffroy St. Hilaire conceived to repre- 

 sent the torpedo's batteries), inasmuch as this system also co-exists in 

 the torpedo with the electric organs. 



That the tail-organs already spoken of, as discovered by Stark, and 

 since so well anatomised by Goodsir, Robin, Leydig, Ecker, Remak, 



