8 2 Memoir Sears Foundation for Marine Research 



Actually, however, it is a matter of common knowledge that they are more loosely 

 aggregated than the foregoing would suggest (Fig. 25F) and that they vary in cross 

 section from hexagonal with rounded corners to roughly circular. The number of 

 columns in a single organ ranges from as few as 140—150 in some genera (Temera and 

 Discopyge) up to an average of 1,025—1,083 for Torpedo nobiliana.'' 



Each column is divided by transverse partitions into a large number of so-called 

 electric discs, each consisting of a clear jelly-like mass that includes a number of large 

 nuclei and each being separated from its neighbors by a connective tissue layer through 

 which run the nerve fibers and blood vessels. Since there may be 375 or more discs 

 per column, their total number in the larger species* is in the hundreds of thousands 

 for each organ. It has been stated that both the final number of columns in the organ 

 and the numbers of electric plates per column are established before birth. But a slight 

 increase In the number of columns takes place with growth, 267, 276, and 315 having 

 been counted for each organ on three embryos of Narcine brasiliensis from Florida, 

 250, 382, and 409 for three adults. Also, It has been found that the number of plates 

 per column varies according to the length of the column ; in one embryo of Narcine 

 brasiliensis the average counts were 305 near the Inner and thicker edge of the organ 

 but only 179 per column near the outer and thinner edge; the counts were 482 and 288 

 respectively In the organ of another.^ 



The nerve supply to the electric organs Is highly developed, each organ receiving 

 one branch of the trigeminal nerve and four branches of the vagus nerve; the former 

 and the three anterior branches of the latter are as thick as the spinal cord and all arise 

 together from a special lobe of the brain known as the "lobus electricus." Distally, 

 these nerves branch again and again and terminate in a cluster of fine fibrils on the 

 ventral connective tissue wall of each electric plate. It has been found that the ventral 

 sides of the plates are negative (electrically speaking) to the dorsal sides, and that the 

 lower side of each electric organ as a whole is negative, thus representing the plus or 

 anode pole of what appears to be a form of multiple concentration cell. In other words, 

 the discharge produced by the organ as a whole passes through the latter from the 

 ventral side toward the dorsal, whereas in an Electric Eel {Electrophorus) it runs through 

 the organ from the tail toward the head, in an Electric Catfish {Malopterurus) from 

 front to rear. All parts of a single organ, and the two organs as well, discharge 

 almost simultaneously, and it has been observed repeatedly that the discharge Is ac- 

 companied by slight muscular contractions of the disc, cupping the margins of the 

 latter upward. 



The ability of Electric Rays to produce shocks was "well known to the ancient 

 Greeks and Romans,"!" ^iX^di it has been known for many years that the discharge has 



7. For a table of average numbers of columns in different species, see Fritsch (Elektr. Fische, 2, 1890: 97; nobiliana 

 listed as "hebetans"); also Ballowitz and Schmidt (in Bolk and others, Handb. Vergl. Anat. Wirbelt., 5, 1938: 669). 



8. The number per organ for a specimen of the European Torpedo marmorata was 179,625, as calculated by Fritsch 

 (Elektr. Fische, 2, 1890: 102). It may reach 500,000 in large specimens of other species of the genus. 



9. Cox and Breder, Zoologica N. Y., 28, 1943: 46. 



10. For further details, see Norman and Eraser (Giant Fishes, 1937: 66). 



