250
THE BIOLOGY OF EUPHAUSIIDS
animal already actively luminescing. If the animal is optically
stimulated so that luminescence is produced and ends before further
optical stimulation then fatigue sets in. Further, a full luminescent
response to a second stimulus will not be produced unless the animal
has been allowed to rest for 5-1 0 min in the dark after the first luminescent response has ended. There is little fatigue, however, associated
with repeated inhibition of luminescence by photoflash. Kay suggests
that the inhibitory processes may be more sensitive than the mechanisms
for producing luminescence through optical stimulation and points out
that isolated photophores can produce some thousands of luminescent
responses thus indicating the presence of much chemiluminescent
material and suggesting that the origin of fatigue must be in some part
of the control system rather than an increasing scarcity of chemiluminescent substance. He therefore postulates the presence of a
neurosecretory mechanism which would initiate the photophore, via
the blood stream, to luminesce and of a nervous control of the inhibitory
processes. Tett (1969) examined the effects of temperature on the
luminescence of ThysanoEssa raschii stimulated by a photoflash. He
measured the delay time between the stimulus and the luminescent
response, the duration of the response, and the time between the
stimulus and the end of the response (delay + duration). These
parameters are all inversely related to temperature. A second stimulus
changed the nature of the response when compared to the first response,
but further stimuli produced no further change, thus supporting Kay’s
division of stimuli into an initial excitatory stimulus and later inhibitory
stimuli. Tett thinks that the flash stimulus produces a simultaneous
inhibition and excitation of luminescence. Initially, the inhibition is
stronger than the excitation so producing the delay period between the
stimulus and the response; the inhibition is of shorter period than the
excitation and so when the inhibition declines the excitation becomes
dominant and the luminescent response is produced. This hypothesis
does not require any special physiological mechanisms for inhibition
and excitation although Tett, like Kay, considers that inhibition
produced by the photoflash is nervous because of its immediate effect.
Euphausiids, under natural conditions in the sea, will not receive an
optical stimulus of light of the order of magnitude of the photoflash.
The intensity of the luminescence from a single animal is of the order
of 2 x
pWIcm2 measured a t a distance of 10 cm (Kampa and
Boden, 1957 ; Kay, 1965). Most investigations of bioluminescence in
the sea have been associated with studies of deep- or sonic-scattering
layers and measurements of the spectral distribution and intensity of
ambient light and of the bioluminescence associated with the scattering
THE BIOLOGY OF EUPHAUSIIDS
animal already actively luminescing. If the animal is optically
stimulated so that luminescence is produced and ends before further
optical stimulation then fatigue sets in. Further, a full luminescent
response to a second stimulus will not be produced unless the animal
has been allowed to rest for 5-1 0 min in the dark after the first luminescent response has ended. There is little fatigue, however, associated
with repeated inhibition of luminescence by photoflash. Kay suggests
that the inhibitory processes may be more sensitive than the mechanisms
for producing luminescence through optical stimulation and points out
that isolated photophores can produce some thousands of luminescent
responses thus indicating the presence of much chemiluminescent
material and suggesting that the origin of fatigue must be in some part
of the control system rather than an increasing scarcity of chemiluminescent substance. He therefore postulates the presence of a
neurosecretory mechanism which would initiate the photophore, via
the blood stream, to luminesce and of a nervous control of the inhibitory
processes. Tett (1969) examined the effects of temperature on the
luminescence of ThysanoEssa raschii stimulated by a photoflash. He
measured the delay time between the stimulus and the luminescent
response, the duration of the response, and the time between the
stimulus and the end of the response (delay + duration). These
parameters are all inversely related to temperature. A second stimulus
changed the nature of the response when compared to the first response,
but further stimuli produced no further change, thus supporting Kay’s
division of stimuli into an initial excitatory stimulus and later inhibitory
stimuli. Tett thinks that the flash stimulus produces a simultaneous
inhibition and excitation of luminescence. Initially, the inhibition is
stronger than the excitation so producing the delay period between the
stimulus and the response; the inhibition is of shorter period than the
excitation and so when the inhibition declines the excitation becomes
dominant and the luminescent response is produced. This hypothesis
does not require any special physiological mechanisms for inhibition
and excitation although Tett, like Kay, considers that inhibition
produced by the photoflash is nervous because of its immediate effect.
Euphausiids, under natural conditions in the sea, will not receive an
optical stimulus of light of the order of magnitude of the photoflash.
The intensity of the luminescence from a single animal is of the order
of 2 x
pWIcm2 measured a t a distance of 10 cm (Kampa and
Boden, 1957 ; Kay, 1965). Most investigations of bioluminescence in
the sea have been associated with studies of deep- or sonic-scattering
layers and measurements of the spectral distribution and intensity of
ambient light and of the bioluminescence associated with the scattering