. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 410 Comparative Animal Physiology a wave length of 474 /x, in a spectrum uncorrected for energy.^*'" Hecht^^- ^-^ measured the spectral sensitivity of the photic response of the clams Mya and Pholas in relation to broad regions of the spectrum. He found a maxi- mum for Mya at 490 /i, and for Pholas at 555 /a, with perhaps another maximum in the ultraviolet. The spectral sensitivity of the squid retina sug- gests that the photosensitive pigment involved is similar to the vertebrate pigment, rhodopsin. Bliss,
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 410 Comparative Animal Physiology a wave length of 474 /x, in a spectrum uncorrected for energy.^*'" Hecht^^- ^-^ measured the spectral sensitivity of the photic response of the clams Mya and Pholas in relation to broad regions of the spectrum. He found a maxi- mum for Mya at 490 /i, and for Pholas at 555 /a, with perhaps another maximum in the ultraviolet. The spectral sensitivity of the squid retina sug- gests that the photosensitive pigment involved is similar to the vertebrate pigment, rhodopsin. Bliss,^^' ^^' ^^ isolated a pigment from squid retinae which resembles the vertebrate rhodopsin (Fig. 118). The absorption maximum is 495 ix, and its absorption spectrum agrees well with the absorption spectrum of visual purple and with the spectral sensitivity of the photoreceptor. There is, how-. 500 W»VP-lrn«th (m/i) Fig. 118. Action spectrum of the dark-adapted human eye (after Ludvigh,"") com- pared with the spectral absorption curve of visual purple. From ; ever, one difficulty in assigning to this pigment a principal role in the visual process; the squid pigment is light stable. Bleaching in the presence of light occurs only when the extracted pigment is sensitized by a dilute denaturant, such as formalin. The bleaching product is identical with visual yellow of the rhodopsin cycle (page 411) and the carotenoid has been identified as retinene]. The spectral sensitivity of several arthropod eyes,"*"- ^^' ""• '""* de- termined by electrical (see page 422) and behavior methods,^"'' indicates ab- sorption maxima in the blue portion of the visible spectrum, and a second maximum in the ultraviolet, wave length 385 /x, for Drosophila and the bee.'"' ^' High concentrations of vitamin A have been isolated from the eyes of several marine Crustacea, the green and fiddler crabs and lobster, and from the eyes of the fresh-wa
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