476 Presents. [Feb. 25, 



The structures of the organs of the skate and torpedo are compared 

 at length, and it is shown that in the case of the torpedo all the 

 non-essential structures are absent, while the all-essential part, the 

 electric layer or plate, closely resembles the corresponding layer or 

 plate in the skate, the electric layer of R. circularis being especially 

 like that of the torpedo. 



In considering the modifications of the electric organ in the skate 

 genus, it is shown that in all the British species, with the exception 

 of R. radiata, R. circularis, and R. fullonica, the elements are in the 

 form of discs. In the three exceptions the elements are more or less 

 cup-shaped. In R. radiata, as described in a former paper, they are 

 in the form of thick-walled shallow cups. The electric plate, ap- 

 parently a greatly enlarged motor plate, lines the cup, which through- 

 out resembles an ordinary striated muscle. In R. circularis, a more 

 specialised member of the group, the electric elements are larger and 

 better developed. The cups are deep and well moulded, and the 

 electric layer is even more complex than in R. batis ; at least, it more 

 closely resembles the electric layer of the torpedo. Further, the 

 cups are invested by a thick nucleated cortex, from which a number 

 of delicate short processes project the first appearance of the long 

 prongs found in R. batis. In R. fullonica the electric elements stand 

 nearly midway between the only partially transformed muscular 

 fibres of R. radiata and the complex discs of R. batis. The cups in 

 JR. fullonica are less deep than in R. circularis and while the electric 

 and striated layers appear to be all but identical in the two species, 

 the cortex is decidedly more like that of R. batis. The short simple 

 processes of R. circularis are represented in R. fullonica by processes, 

 often complex, which, by projecting freely from the outer surface of 

 the cup, give it an irregular villous appearance, and at once suggest 

 the processes or prongs which are so characteristic of the alveolar 

 layer of R. batis. 



After giving a summary of his observations on the electric organ 

 of the skate, the author concludes by pointing out that it is not yet 

 possible to indicate by what method the electric organs of fishes have 

 been produced. 



Presents, February 25, 1892. 

 Transactions. 



Baltimore: Johns Hopkins University. Studies (Historical and 

 Political Science). Series 10. Nos. 2-3. 8vo, Baltimore 1892. 



The University. 



Brussels : Acadenrie Royale de Medecine de Belgique. Memoires 

 Couronnes et autres Memoires. Tome X. Fasc 5. Tome XI. 

 Fasc 1. 8vo. Bruxelles 1892. The Academy. 



