The Origin of the Electric Organs in Astroscopus Guttatus. 143 



STRUCTURAL. 



The general structure of the organs in Torpedo had been described in 

 1678 by Lorenzini (TO), and a detailed account was published in 1835 by 

 John Hunter (63), but the anatomy of the electric organs in general was 

 not given much consideration by investigators until the discovery, 

 by Bilharz, in 1857 (16), of the electrical plates in Gymnolus. Ballowitz 

 worked out the fine anatomy of the electric organs of Torpedo, Gymno- 

 tus, and the Raj idee, to the latter of which he gave the name of the 

 "pseudoelectric fishes," and to the organs the name of the "pseudo- 

 electric organs/' inasmuch as their structure resembled that of other 

 electric organs, while their function was not then known. Ogneff (75) 

 and Max Schultze (85) made careful and accurate observations of the 

 innervation of these organs and of the finer details of the nerve-endings 

 of the same. 



The peculiar structure common to all electric fishes is the semi- 

 transparent material, of the consistency of jelly, which lies between 

 and around the electroplaxes and in which lie the connective-tissue 

 septa and numerous nerve-branches. In Torpedo these are two large 

 masses, concave on the inner border and divided by septa into hexago- 

 nal columns, the ends of which lie under the dorsal and ventral surfaces 

 of the skin. In Torpedo occidentalis there are 1,969 columns, in Tor- 

 pedo ocellata but 450 (Gotch so). 



In Raja there are two very slender organs, tapering at both ends and 

 lying one on each side of the spinal column. These organs are formed 

 from and lie embedded in the muscles of the tail. 



In Gymnolus there are four such organs, two dorsal and two ventral, 

 of which the dorsal are the larger. The organs are divided into col- 

 umns which run variable distances from the cephalic end to the tip of 

 the tail of the fish, which may be from 8 to 10 feet in length. 



Mormyrus has four organs formed from and replacing the posterior 

 regions of the muscles of the tail. The long diameter is parallel to the 

 spinal column, and with the general position very like that of the 

 organs in Gymnotus, though not extending so far into the anterior end 

 of the body. In Gymnarchus there are eight cylindrical organs, four 

 on each side, embedded in the muscle-tissue of the tail, as close to the 

 median bony parts as a little connective tissue in between will permit. 



The organ of Malopterurus is peculiarly situated in the thickened 

 skin and is imperfectly divided into halves by a connective-tissue sep- 

 tum on the ventral surface. It enwraps the whole body except the 

 fins and the head. 



The finer anatomy of the electric organs differs considerably in the 

 different groups. In Malopterurus there is no obvious arrangement 

 into columns, the organ being composed of lozenge-shaped electro- 

 plaxes, dove-tailed into each other and surrounded by the character- 

 istic jelly-like material. Each half of the organ is innervated by a 



