1 64 Papers from the Marine Biological Laboratory at Tortugas. 



the neural canal and its contained spinal cord. This second pair of spindles 

 are at the level of the upper part of the spinal cord. The lower median 

 spindles are found much below, on each side of the ventral processes of the 

 vertebra. They lie at about the level of the caudal artery and almost as 

 widely separated as the upper median pair. Lastly, the ventral pair of 

 spindles are found just below the latter pair and slightly below the level of 

 the caudal vein, which lies between them. They are separated a little less 

 than the lower median pair by the narrower bony structures at this point. 



Fig. 4.- 



Ventral Lower median 



-Diagram showing longitudinal position and extent of electric spindles in Gymnarchus. 

 Tiiose of one side only can be shown in figure. 



The four spindles are largest in diameter in the tail, especially out in the 

 thick, finger-like, naked extremity. From this part they taper to a smaller 

 size as they go forward in the body and they finally become thin and end at 

 points in the neighborhood of the anal opening (see text-fig. 4). All are not 

 of equal length. As Fritsch has shown, the dorsal organ is the shortest and 

 extends for about 20 cm. in a fish of 89 cm. length. The ventral pair reach 

 for about 5 cm. further, or 25 cm. in length in a fish of the same size. The 

 two median spindles reach for about 40 cm. from the tip of the tail. 



Each spindle is marked off clearly from the neighboring muscle, and other 

 tissues which are found next to it, by a distinct connective-tissue covering. 

 In my largest specimen, which is a young fish of 40 days, this is well shown 

 and is exactly like other dividing connective-tissue sheaths that surround 

 the various muscle divisions. Like them, it often contains pigment cells 

 which show golden-brown pigment granules. 



The important contents of these spindles are alternate, cylindrical 

 segments of a denser, deeper-staining, muscle-like substance, the electro- 

 plaxes; and a connective tissue of jelly-like, grayish transparence which in 

 all ways appears to be similar to the "electric connective-tissue" found 

 between the electroplaxes in the other electric fishes. In this tissue are 

 found the blood-supply, which is largely in contact with the ends of the 

 electroplaxes, principally the anterior end; and the nerve-supply of thick, 

 meduUated fibers which run towards, and are attached to, the posterior 

 ends of these organs. In this case, according to both Pacini's law and the 

 fish's relationship to Mormyrus, the direction of the current at time of 

 discharge should be from tail towards the head. I have been unable to 

 learn, from the literature of travelers and scientific collectors and observers, 

 if the electric discharge is strong enough to be felt by the hand. Budgett 

 does not mention it, and no other does, so I conclude that it is not a strong 

 shock and that the organ must be classed with the weak electric organs, 



