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M. V. L. BENNETT
Fig. 16. A tonic electroreceptor of the transparent catfish Kryptopterus. The
tissue is not fixed or dissected. The receptor is located on the caudal fin between fin
rays ( F ) ; anterior is to the left. The receptor cavity opens to the exterior at the
arrow. Receptor cells ( R ) can be seen in the cavity. A receptor on the other side
of the fin is out of focus. Striations of muscle fibers ( M ) are visible on the left.
tential, and most of a long-lasting voltage pulse applied at the receptor
opening is developed across their inner rather than their outer faces, i.e.,
the inner faces are of higher resistance (they also have a longer time
constant). Nerve impulses can be recorded either in the receptor cells
or extracellularly just deep to the receptor cells, and the responses and
sensitivity are similar to those of tonic electroreceptors of gymnotids
and mormyrids.
Responses have also been recorded from afferent fibers of electroreceptors in Amiurus ( Roth, 1968, 1969). Adaptation appears to be somewhat more rapid than in the gymnotid and mormyrid tonic receptors, and
responses to maintained stimuli are quite small.