5. TEMPERATURE RECEPTORS
123
warming, which corresponds to a change of 0.05"-0.1"C. Although
Bardach and Bjorklund did not specifically test for this, it is probable that
it is the change away from the previous temperature (albeit a slow one)
to which the fish responded, rather than to an absolute temperature level,
since responses of trout, Salvelinus, in temperature gradients are known
to depend on their previous thermal history (Sullivan, 1954).
From Table I it appears that the threshold for marine fish is lower
than that of freshwater fish, but the differences are more likely to be
caused by the interests, or patience, of the experimenters. For example,
Dijkgraaf (1940) did not attempt to find absolute thresholds.
The comparable evidence for the sensitivity of elasmobranch fishes is
lacking.
Amphioxus has an escape response to warming of the skin in the
region of the dorsal fin, which can be elicited by a rise of 0.75OC in 3
sec or by 3°C in 20 sec (Lele et al., 1958).
111. THE SENSE ORGANS INVOLVED
Two alternative sensory systems have been proposed as the thermoreceptors responsible for the results described in the previous section;
namely, the lateral line organs and the general, cutaneous, segmental
innervation. Historically, the lateral line came first, following the pioneering electrophysiological investigations of Hoagland ( summarized in
Hoagland, 1935). He had found that the "spontaneous" discharge increased at higher temperatures, and in the absence of cutaneous sensitivity, he attributed thermoreception to the lateral line. This suggestion
was followed up by behavioral experiments (Rubin, 1935; see below).
Since that time, much of the effort of later workers has been devoted to
the demonstration that the lateral line is not involved, but rather the
segmental cutaneous system. A thermoreceptor function of the lateral line
is unlikely in view of its known mechano- and electroreceptor functions
(see chapters by Flock and Bennett, this volume), although arguments
based on strict, single-modality functioning of receptors are not so valid
today as was once thought.
However, there is clear evidence on this point from conditioning experiments (Dijkgraaf, 1940). Minnows, Phoxinus laevis, which had been
trained to respond differentially to streams of warm or cold water applied
by pipette to the flank, responded as usual if the lateral line nerves had
been cut; but they failed to respond if the site of stimulation was
123
warming, which corresponds to a change of 0.05"-0.1"C. Although
Bardach and Bjorklund did not specifically test for this, it is probable that
it is the change away from the previous temperature (albeit a slow one)
to which the fish responded, rather than to an absolute temperature level,
since responses of trout, Salvelinus, in temperature gradients are known
to depend on their previous thermal history (Sullivan, 1954).
From Table I it appears that the threshold for marine fish is lower
than that of freshwater fish, but the differences are more likely to be
caused by the interests, or patience, of the experimenters. For example,
Dijkgraaf (1940) did not attempt to find absolute thresholds.
The comparable evidence for the sensitivity of elasmobranch fishes is
lacking.
Amphioxus has an escape response to warming of the skin in the
region of the dorsal fin, which can be elicited by a rise of 0.75OC in 3
sec or by 3°C in 20 sec (Lele et al., 1958).
111. THE SENSE ORGANS INVOLVED
Two alternative sensory systems have been proposed as the thermoreceptors responsible for the results described in the previous section;
namely, the lateral line organs and the general, cutaneous, segmental
innervation. Historically, the lateral line came first, following the pioneering electrophysiological investigations of Hoagland ( summarized in
Hoagland, 1935). He had found that the "spontaneous" discharge increased at higher temperatures, and in the absence of cutaneous sensitivity, he attributed thermoreception to the lateral line. This suggestion
was followed up by behavioral experiments (Rubin, 1935; see below).
Since that time, much of the effort of later workers has been devoted to
the demonstration that the lateral line is not involved, but rather the
segmental cutaneous system. A thermoreceptor function of the lateral line
is unlikely in view of its known mechano- and electroreceptor functions
(see chapters by Flock and Bennett, this volume), although arguments
based on strict, single-modality functioning of receptors are not so valid
today as was once thought.
However, there is clear evidence on this point from conditioning experiments (Dijkgraaf, 1940). Minnows, Phoxinus laevis, which had been
trained to respond differentially to streams of warm or cold water applied
by pipette to the flank, responded as usual if the lateral line nerves had
been cut; but they failed to respond if the site of stimulation was