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ELECTRIC ORGANS
M . V. L. BENNETT
I. Introduction .
. . . . . . . . . . . 347
11. Electric Organs and Electrocytes
. . . . . . . 355
A. Methods . . . . . . . . . . . . 355
B. Membrane Properties
. . . . . . . . . 357
C. Marine Electric Fish
. . . . . . , . . 362
D. Freshwater Electric Fish
. . . . . . . . 380
E. Some Quantitative Considerations
.
. . . . . 448
F. Adaptation and Convergent Evolution in Electric Organs . . 450
G. Embryonic Origin and Developmerlt of Electric Organs . . 455
H. Electrocytes as Experimental Material
. . . . . 457
111. Neural Control of Electric Organs
. . . . . . . 460
A. Pathways and Patterns of Neural Activity .
. . . . 465
B. Synchronization of Electrocyte Activity
. . . . . 475
C. Organization of Electromotor Systems . . . . . . 478
IV. Conclusions and Prospects . . . . . . . . . 483
References
. . . . . . . . . . . . . 484
I. INTRODUCTION
Electric organs are organs specialized for the production of an electric
field outside the body. They are found only in fish but apparently have
evolved independently in some six different groups ( Fig. 1 and Table I ) .
Electric fish are conveniently divided into two types, strongly and weakly
electric. The discharge of a strongly electric fish is so large that the fish
is painful to handle; the electric organ presumably or demonstrably functions as a weapon either defensively against predators or offensively in
securing food. A weakly electric fish produces potentials that are too
small to have value offensively or defensively; their organs function ( a t
least in freshwater species) as part of an electrosensory system. The fish
detects objects by means of the distortions they cause in the field set up
by the electric organ. The sensing elements are the electroreceptors
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