238
THE BIOLOGY OF EUPHAUSIIDS
white light, of digitonin extracts of the eyes of five species of
euphausiids. The following absorption maxima, indicating the presence
of rhodopsin visual pigments were found : Meganyctiphanes norvegica,
460-465 mp ; Thysanoessa raschii, 460-465 mp ; Thysanopoda acutifrons,
480 mp ; Nematoscelis megalops, 465 mp ; Stylocheiron maximum, 470 mp.
Kampa (1955) identified a visual pigment which she called euphausiopsin
in the eyes of Euphausia pacijica and the maximum of its difference
curve was between 460 and 465 mp. Since these results were published,
however, D. J. Pritchard re-examined the visual pigments of Meganyctiphanes norvegica and obtained evidence of a rhodopsin with an absorption maximum a t 528 mp, considerably higher than the previously
reported absorption maxima. This is a single experiment and little
stress should be placed on this result until further analyses have been
made.
Investigations of the vision of euphausiids have been made by
examining the spectral bands of light to which the eyes are most sensitive. Kampa et al. (1959) were able to measure the electrical potentials
developed in the eyes of Euphausia pacijica, Nematoscelis dificilis and
Meganyctiphanes norvegica when exposed to flashes of white light. The
electroretinograms of the upper and lower lobes of the bilobed eyes of
species such as Nematoscelis dificilis and Thysanoessa gregaria are
quite different. The main wave of the upper lobe is a fast response,
lasting 20-30 msec, whose duration and amplitude are not dependent
on the duration and amplitude of the stimulus whereas the main wave
of the lower lobe is a slow response whose duration, but not amplitude,
varies with the duration of the stimulus. Spherical eyes of species such
as Euphausia pacijica and Meganyctiphanes norvegica exhibit both fast
and slow responses to stimuli and, as in bilobed eyes, the duration of the
fast response is independent of the duration of the stimulus but the
duration of the slow response is directly related to the duration of the
stimulus (Boden et al., 1961). The amplitudes of the fast and slow
responses vary directly with the logarithms of the stimulating intensities
through a range of two orders of magnitude (Fig. 84). They then
examined the spectral sensitivities of the eyes of three species and
found that the upper and lower lobes of the eye of Nematoscelis dificilis
have different response curves (Fig. 84). The upper lobe is most sensitive
to light of wavelength 460-470 mp and has a further smaller peak of
sensitivity a t about 530mp while the lower lobe shows maximal
sensitivity over a wide range of wavelength, from 460-515 mp, and is
especially sensitive to wavelengths near 490 mp. They have superimposed the difference spectrum of euphausiopsin on the spectral
sensitivity curve of the upper eye and the close relationship between
THE BIOLOGY OF EUPHAUSIIDS
white light, of digitonin extracts of the eyes of five species of
euphausiids. The following absorption maxima, indicating the presence
of rhodopsin visual pigments were found : Meganyctiphanes norvegica,
460-465 mp ; Thysanoessa raschii, 460-465 mp ; Thysanopoda acutifrons,
480 mp ; Nematoscelis megalops, 465 mp ; Stylocheiron maximum, 470 mp.
Kampa (1955) identified a visual pigment which she called euphausiopsin
in the eyes of Euphausia pacijica and the maximum of its difference
curve was between 460 and 465 mp. Since these results were published,
however, D. J. Pritchard re-examined the visual pigments of Meganyctiphanes norvegica and obtained evidence of a rhodopsin with an absorption maximum a t 528 mp, considerably higher than the previously
reported absorption maxima. This is a single experiment and little
stress should be placed on this result until further analyses have been
made.
Investigations of the vision of euphausiids have been made by
examining the spectral bands of light to which the eyes are most sensitive. Kampa et al. (1959) were able to measure the electrical potentials
developed in the eyes of Euphausia pacijica, Nematoscelis dificilis and
Meganyctiphanes norvegica when exposed to flashes of white light. The
electroretinograms of the upper and lower lobes of the bilobed eyes of
species such as Nematoscelis dificilis and Thysanoessa gregaria are
quite different. The main wave of the upper lobe is a fast response,
lasting 20-30 msec, whose duration and amplitude are not dependent
on the duration and amplitude of the stimulus whereas the main wave
of the lower lobe is a slow response whose duration, but not amplitude,
varies with the duration of the stimulus. Spherical eyes of species such
as Euphausia pacijica and Meganyctiphanes norvegica exhibit both fast
and slow responses to stimuli and, as in bilobed eyes, the duration of the
fast response is independent of the duration of the stimulus but the
duration of the slow response is directly related to the duration of the
stimulus (Boden et al., 1961). The amplitudes of the fast and slow
responses vary directly with the logarithms of the stimulating intensities
through a range of two orders of magnitude (Fig. 84). They then
examined the spectral sensitivities of the eyes of three species and
found that the upper and lower lobes of the eye of Nematoscelis dificilis
have different response curves (Fig. 84). The upper lobe is most sensitive
to light of wavelength 460-470 mp and has a further smaller peak of
sensitivity a t about 530mp while the lower lobe shows maximal
sensitivity over a wide range of wavelength, from 460-515 mp, and is
especially sensitive to wavelengths near 490 mp. They have superimposed the difference spectrum of euphausiopsin on the spectral
sensitivity curve of the upper eye and the close relationship between