10. ELECTRIC ORGANS
349
and experience of shocks. The Torpedo and electric eel were studied by
many early physiologists, but the stargazer escaped the attention of
the scientific community until just before Dahlgren and Silvester described its organ in 1906.
Recognition of weakly electric fish was relatively delayed because of
the imperceptibility of their discharges, and the electric activity of many
was unknown until the 1950s (Lissmann, 1951, 1958; Coates et al., 1954;
Grundfest, 1957). Howcver, all the groups had been recognized from
morphological evidence by the early 1900s although their organs were
sometimes classified as “pseudoelectric.” Historical references are given
in the earlier reviews by Grundfest (1957) and Keynes (1957), and
the historical essays of Kellaway (1946) and Mauro (1969) are charming. Relatively brief reviews of recent work are given in Bennett (1970)
and Grundfest ( 1967).
Electric fish have been studied in part because of their remarkable
physiological abilities and the ease of detection of their discharges. Also,
it has been hoped that they might reveal a great deal about normal
function. The argument is that evolution may have exaggerated some
aspect of organ or cell that makes a general phenomenon more understandable or easier to study. The giant axon of the squid is an outstanding example of a cell that has evolved in such a way-toward increased
size-that makes feasible many kinds of experiments that are much more
difficult in other tissues ( Hodgkin, 1964).
The generating cells of electric organs are modified from muscle fibers
except in the sternarchid family of the larger group, the gymnotids. In
the sternarchids the myogenic part of the organ has been lost and thc
organ is modified from nerve fibers; that is, it is neurogenic. The evidence
of origin will be discussed in Section II,G,l,f. In a number of species the
generating cells are flattened and for this reason have been termed
electroplaque( s ) , electroplate( s ) , or clectroplax( es). However, in many
of the more recently described organs, the generating cells have quite
complex shapes. Although electroplaque still seems a natural term for
flattened cells, the author has introduccd the more general term electrocyte to refer to any generating cell whatever its shape (Bennett, 1970).
Electric organs generally are rather gelatinous, and a large fraction of
their volunic is extracellular space. They contain a considerable amount
of connective and other accessory tissues as well as blood vessels and
motor nerves that control the discharge. As will be seen below the connective tissue can be important in channeling the flow of current.
Electrocytes work on the same general principles as ordinary nerve
and muscle cells: potentials are generated across membranes. In all
known cases the potentials result from selective permeability and passive
movement of ions down their concentration gradients. But it is likely
349
and experience of shocks. The Torpedo and electric eel were studied by
many early physiologists, but the stargazer escaped the attention of
the scientific community until just before Dahlgren and Silvester described its organ in 1906.
Recognition of weakly electric fish was relatively delayed because of
the imperceptibility of their discharges, and the electric activity of many
was unknown until the 1950s (Lissmann, 1951, 1958; Coates et al., 1954;
Grundfest, 1957). Howcver, all the groups had been recognized from
morphological evidence by the early 1900s although their organs were
sometimes classified as “pseudoelectric.” Historical references are given
in the earlier reviews by Grundfest (1957) and Keynes (1957), and
the historical essays of Kellaway (1946) and Mauro (1969) are charming. Relatively brief reviews of recent work are given in Bennett (1970)
and Grundfest ( 1967).
Electric fish have been studied in part because of their remarkable
physiological abilities and the ease of detection of their discharges. Also,
it has been hoped that they might reveal a great deal about normal
function. The argument is that evolution may have exaggerated some
aspect of organ or cell that makes a general phenomenon more understandable or easier to study. The giant axon of the squid is an outstanding example of a cell that has evolved in such a way-toward increased
size-that makes feasible many kinds of experiments that are much more
difficult in other tissues ( Hodgkin, 1964).
The generating cells of electric organs are modified from muscle fibers
except in the sternarchid family of the larger group, the gymnotids. In
the sternarchids the myogenic part of the organ has been lost and thc
organ is modified from nerve fibers; that is, it is neurogenic. The evidence
of origin will be discussed in Section II,G,l,f. In a number of species the
generating cells are flattened and for this reason have been termed
electroplaque( s ) , electroplate( s ) , or clectroplax( es). However, in many
of the more recently described organs, the generating cells have quite
complex shapes. Although electroplaque still seems a natural term for
flattened cells, the author has introduccd the more general term electrocyte to refer to any generating cell whatever its shape (Bennett, 1970).
Electric organs generally are rather gelatinous, and a large fraction of
their volunic is extracellular space. They contain a considerable amount
of connective and other accessory tissues as well as blood vessels and
motor nerves that control the discharge. As will be seen below the connective tissue can be important in channeling the flow of current.
Electrocytes work on the same general principles as ordinary nerve
and muscle cells: potentials are generated across membranes. In all
known cases the potentials result from selective permeability and passive
movement of ions down their concentration gradients. But it is likely