Fishes of the Western North Atlantic 8 1 



several rows in function simultaneously; the integument bearing the tooth bands firmly 

 attached to jaw cartilages in some, only loosely so in others. 



Skin soft and entirely naked in most species, but with margins of pectorals de- 

 scribed as having small papillae "partly spinous" in one.^ 



Rostral projection of cranium single or double and more or less branching in 

 some; reaching to anterior margin of disc. Antorbital cartilages extending forward to 

 support front of disc, their anterior margins dissected in complex fashion in some 

 species but less so in others, and spreading laterally to anterior rays of pectorals or 

 even overlapping latter.* Extremities of branchial rays widely expanded as plate-like 

 discs. Dorsal and caudal fins supported basally by short cartilaginous radials, distally 

 by much more numerous fine horny rays (ceratotrichia) in double series. Pectoral and 

 pelvic fins without horny rays, the cartilaginous radials extending outward to margins. 

 Pelvis (in species studied) bowed rearward, with a well developed lateral process ex- 

 tending forward at either end. Margins of gill arches smooth inward from gill filaments. 

 Electric organs well developed, between sides of head and forward extensions of pec- 

 torals. 



Electric Organs. The anatomy and physiology of the electric organs of the Tor- 

 pedo Rays, as well as of those of other fishes, and the characteristics of the electric cur- 

 rents generated by them, have been the subject of much research, resulting in extensive 

 literature.^ Each of the two organs of an Electric Ray occupies one side of the anterior 

 part of the disc between the anterior extension of the pectoral and the head, extending 

 forward about to the level of the eye and rearward past the gill region to the vicinity 

 of the pectoral girdle. Together the two organs comprise about one-sixth of the total 

 weight of the fish in each of the two western Atlantic species {Torpedo nohiliana and 

 Narcine brasilioisis) for which this relationship has been determined. In most cases the 

 outlines of the organs are visible externally on the ventral side and usually faintly so 

 on the dorsal side as well, where, however, they are more hidden from view by the 

 pigmentation of the skin. 



Numerous columnar structures, separated by loose fibrous tissue, make up each 

 organ and occupy the entire thickness of the disc from the upper to the lower integu- 

 ment, their lengths decreasing toward the periphery as the disc becomes thinner. These 

 columns, often referred to as "prisms," have been described repeatedly and have been 

 pictured more or less diagramatically as arranged like the cells of a honeycomb.* 



3. Torpedo mackayana Metzelaar (Trop. Atlant. Visschen, 1919: 197). 



4. For a recent discussion of the head skeleton and comparison with other batoids, see Holmgren (Acta Zool. Stockh., 

 22, 1941 : 57, 65, 66). 



5. For general summaries of results and references, see Gotch (in Shafer, Text Bk. Physiol., 1900: 561-591) and espe- 

 cially Garten (in Wintersheim, Handb. Vergl. Physiol., 3 [2], 1910-1914: i72fF). For more detailed accounts, see 

 Gotch (Philos. Trans., [B] 17S, 1888: 487-537; [B] 179, 1889: 329-363), Schoenlein (Z. Biol., 31, N. S. 13, 1895: 

 449-523), Fuji (J. CoU. Sci. Tokyo, J7, 1914: i), as well as Coates and Cox (Zoologica N. Y., 27, 1942: 25), and 

 Cox and Breder (Zoologica N. Y., 28, 1943: 45) for observations on the discharges of Torpedo nohiliana and of 

 Narcine brasiliensis respectively. 



6. For semidiagrammatic illustrations of the arrangement of the columns in various species, see especially Fritsch 

 (Elektr. Fische, 2, 1890: pis. 3-15). For a more realistic illustration of their actual appearance in Torpedo when 

 exposed to view, see Jobert (Appar. Electr. Poissons, 1858: pi. i, figs. 1-3). 



