THE GYMNOTID EELS OF TROPICAL AMERICA. 



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found only in the posterior half of the fish. The large organ of each side is more 

 or less quadrant shaped in cross-section, and is of greatest diameter about a centi- 

 meter back of its origin. It tapers gradually back of this point becoming more 

 nearly circular in cross-section until it disappears a few centimeters from the end 

 of the tail. It lies on each side of the hsemal spine above the anal fin musculature 

 and below the muscle ventralis. In the region of its maximum size the top of each 

 organ is on a level with the vertebral centra, but as the caudal end is approached, 

 the dorsal portion of each organ lies more and more ventrad. 



The organ of Sachs consists of a series of bundles of fibers which resemble both 

 muscle and electric tissue. From the middle of the body to the caudal end of the 

 large electric organs, the organs of Sachs lie on the dorso-lateral surface of the 

 latter, just below the muscle ventralis. The bundles of this organ wrap around the 

 large electric organ obliquely in a latero-ventral direction. They extend farther 

 ventrad as the caudal extremities of the large organs are neared. They finally 

 close over the ends of these. The organs of Sachs increase in diameter caudad. 



The organs of Hunter are triangular in cross-section and much smaller than 

 either of the other two pairs of organs. They are in the anal fin region and lie 

 between the muscles pinnalis qnalis externalis and the muscles pinnalis analis 

 internalis. Dorsally they are separated from the large organ by the remnants of 

 the muscles lateralis imus. They taper off as their caudal ends are approached 

 and terminate a few centimeters in front of the ends of the large organs. Plate 

 XIX, figs. 21, 22, 23 represent cross-sections of the electric eel showing these points. 



Both the large organs and the organs of Hunter are composed of plates of tissue 

 which run parallel to the large axis of the fish. In the large organs these plates 

 are more or less arched ventrally in cross-section. In the small organs they are 

 almost flat. The number of these plates seem to be rather constant in each organ, 

 regardless of the size of the fish. Bois-Reymond (in Sachs, Zitteraal, p. 32) gives 

 the following table : 



According to Sachs, who confirmed in general the work of Pacini, the large 

 electric organs are made up of minute units about .14 mm. broad, which lie at right 

 angles to the long axis of the plates. Each unit is divided near the center by a 

 vertical partition. On the anterior face of this are several papillae which do not 

 reach the wall of the unit. On the posterior face are fewer papillae which reach 

 out to the wall of the unit. Between the latter are several minute papillse. It is 



