326
GEORGE WALD
our laboratory has recently made an extensive survey of this ratio in the
retinas of individual animals (44). He finds a wide range of molar ratios
of Ai:A 2 , from 25:75 to 65:35, with an average value (including the
above observations) of Α Χ :Α 2 = 45:55. However he has found also that
porphyropsin possesses a molar extinction only about 3/4 that of
rhodopsin. The ratio of the extinctions of rhodopsin: porphyropsin in
these retinas is therefore on the average about 1.1:1. That is, there is
on the average a slight preponderance of vitamin A 2 , and a slight preponderance, extinction-wise, of rhodopsin, in the Anguitta retina; and
Brown and Brown (39) have found the European Anguitta to resemble
the American in this regard.
The anadromous alewife, Pomolobus pseudoharengus, and white
perch possess vitamin A 2 and porphyropsin alone (30, 43). The permanently brackish water killifish, Fundulus heteroclitus, has a mixture of
both vitamins Ai and A 2 , and of rhodopsin and porphyropsin, predominantly the former, like the eel (43). All the euryhaline forms examined
followed the simple rule that all of them possess either predominantly
or exclusively the vitamin A and visual system characteristic of the
spawning environment.
These observations have been confirmed by a number of workers:
Kampa (34) on the European trout (A max 510 m/x); Collins and Morton
(35) on the char, an anadromous salmonid (A max 514 τημ); Bridges (45)
on the rainbow trout. Carlisle and Denton (46) have found A max of the
visual pigment in the immature European freshwater eel (Anguitta
anguitta) about where we found it in the American species, but have
introduced a further development with regard to this animal, of which
more below.
Munz (47) has reported measurements on a "euryhaline" fish, the
mudsucker (Gillichthys mirabilis), which though possessing a photopigment with the intermediate A max 512 ηΐμ, derives this wholly from
vitamin Ai. It is not clear why Munz speaks of this fish as euryhaline.
He cites earlier work on this species by Kampa (34) and Weisel (48),
both of whom speak of it as a marine teleost. Munz cites Weisel to the
effect that the mudsucker can tolerate salt concentrations "both above
and below that of sea water." I know of no marine fish unable to do the
same. The observation that the rhodopsin of this animal lies unusually
high in A max among marine fishes is interesting, but has little to do with
the present problem.
In summary, the euryhaline fishes that have been examined follow
the rule already stated: they contain in their retinas either mixtures of
vitamins A x and A 2 in which the vitamin A ordinarily characteristic of
the spawning environment tends to predominate, or that vitamin A alone.
GEORGE WALD
our laboratory has recently made an extensive survey of this ratio in the
retinas of individual animals (44). He finds a wide range of molar ratios
of Ai:A 2 , from 25:75 to 65:35, with an average value (including the
above observations) of Α Χ :Α 2 = 45:55. However he has found also that
porphyropsin possesses a molar extinction only about 3/4 that of
rhodopsin. The ratio of the extinctions of rhodopsin: porphyropsin in
these retinas is therefore on the average about 1.1:1. That is, there is
on the average a slight preponderance of vitamin A 2 , and a slight preponderance, extinction-wise, of rhodopsin, in the Anguitta retina; and
Brown and Brown (39) have found the European Anguitta to resemble
the American in this regard.
The anadromous alewife, Pomolobus pseudoharengus, and white
perch possess vitamin A 2 and porphyropsin alone (30, 43). The permanently brackish water killifish, Fundulus heteroclitus, has a mixture of
both vitamins Ai and A 2 , and of rhodopsin and porphyropsin, predominantly the former, like the eel (43). All the euryhaline forms examined
followed the simple rule that all of them possess either predominantly
or exclusively the vitamin A and visual system characteristic of the
spawning environment.
These observations have been confirmed by a number of workers:
Kampa (34) on the European trout (A max 510 m/x); Collins and Morton
(35) on the char, an anadromous salmonid (A max 514 τημ); Bridges (45)
on the rainbow trout. Carlisle and Denton (46) have found A max of the
visual pigment in the immature European freshwater eel (Anguitta
anguitta) about where we found it in the American species, but have
introduced a further development with regard to this animal, of which
more below.
Munz (47) has reported measurements on a "euryhaline" fish, the
mudsucker (Gillichthys mirabilis), which though possessing a photopigment with the intermediate A max 512 ηΐμ, derives this wholly from
vitamin Ai. It is not clear why Munz speaks of this fish as euryhaline.
He cites earlier work on this species by Kampa (34) and Weisel (48),
both of whom speak of it as a marine teleost. Munz cites Weisel to the
effect that the mudsucker can tolerate salt concentrations "both above
and below that of sea water." I know of no marine fish unable to do the
same. The observation that the rhodopsin of this animal lies unusually
high in A max among marine fishes is interesting, but has little to do with
the present problem.
In summary, the euryhaline fishes that have been examined follow
the rule already stated: they contain in their retinas either mixtures of
vitamins A x and A 2 in which the vitamin A ordinarily characteristic of
the spawning environment tends to predominate, or that vitamin A alone.