SOME ASPECTS OF PHOTORECEPTION AND VISION m FISHES
175
overlying chromatophores, or covering the pineal region, have p r o d u d
changes in the responsiveness of Uambwia to light (Breder and Rasquifi,
1960; Raaquin, 1958; Breder, 1959).
B. Pupillmy Movement
Closure of the pupil in light occurs in many elasmobranchs and in a
few teleosts (see Walls, 1942), and some degree of pupiIIary movement,
albeit small, probably occurs in a great many bony fishes. Gilbert
(1961) haa confirmed that pupillary closure is not consensual in sharks ;
i.e. illumination of one eye causes closure of the pupil of that eye and
not of its fellow. Young (1933a) was able to give a physiological
explanation of this effect when he showed that the iris sphincter muscle
of dogfish was not innervated, and it contraded in direct response to
illumination. I n rays (Raia) there is contralaterill lowering of the
operoular flap of an eye when the opposite eye is illuminated (Bateson,
1890b), and this presupposes the existence of a different kind of controlling system in these animals. Pupillary closure is very slight,
variable and negligible in some species. e.g. S q w l w acunthias.
Investigating two teleosts (Uranoscopw and Lophim) having extenaive pupillary excursions, Young (1931a, b, 1933b) found that the
responses are under the control of the autonomic nervous system. The
sphincter is controlled by the sympathetic and the dilatator muscle by
the oculomotor (parasympathetic nervous system). There am some
speoies, however, notably the eel, in which there is a direct response to
light, snd the pupil of the isolated eye closes when it ia illuminated. In
these animals the pigmented smooth muscle fibres of the iris contraot
when stimulated by incident light. Studies of the isolated iris of the eel
have shown that the action spectrum for contraction has a major peak
at 600 mp, and resembles the absorption spectrum for eel rhodopsin
(Seliger, 1962).
C . The Tapetunb Lucidurn of Chondrichthyea
There is a niirror or tapetum lucidum (L. tapete, carpet) in the eye
of chondriohthian fishes, which is responsible for the remarbble eyeshine that they exhibit. Eyezdhine, of course, is most evident in those
species whose pupils remain open when illuminated and in bathypelagic
species with large pupils. The tapetum lucidum contains reflecting cells
that lie in the inner layer of the chorioid, immediately underneath the
ohoriocapillaris (Fig. 2). It is present in most elasmobranch and it
also occurs in holocephalans (Franz, 1905 ; Walls, 1942). It appears to
be absent in the bathybenthic torpedo Benthobat& with rudimentary
eyes ; at least one is not mentioned by Brauer (1908). A tapetum is said
to be lacking in Laemargua (=Somniosw, an abyssal shark), aayliobatM
175
overlying chromatophores, or covering the pineal region, have p r o d u d
changes in the responsiveness of Uambwia to light (Breder and Rasquifi,
1960; Raaquin, 1958; Breder, 1959).
B. Pupillmy Movement
Closure of the pupil in light occurs in many elasmobranchs and in a
few teleosts (see Walls, 1942), and some degree of pupiIIary movement,
albeit small, probably occurs in a great many bony fishes. Gilbert
(1961) haa confirmed that pupillary closure is not consensual in sharks ;
i.e. illumination of one eye causes closure of the pupil of that eye and
not of its fellow. Young (1933a) was able to give a physiological
explanation of this effect when he showed that the iris sphincter muscle
of dogfish was not innervated, and it contraded in direct response to
illumination. I n rays (Raia) there is contralaterill lowering of the
operoular flap of an eye when the opposite eye is illuminated (Bateson,
1890b), and this presupposes the existence of a different kind of controlling system in these animals. Pupillary closure is very slight,
variable and negligible in some species. e.g. S q w l w acunthias.
Investigating two teleosts (Uranoscopw and Lophim) having extenaive pupillary excursions, Young (1931a, b, 1933b) found that the
responses are under the control of the autonomic nervous system. The
sphincter is controlled by the sympathetic and the dilatator muscle by
the oculomotor (parasympathetic nervous system). There am some
speoies, however, notably the eel, in which there is a direct response to
light, snd the pupil of the isolated eye closes when it ia illuminated. In
these animals the pigmented smooth muscle fibres of the iris contraot
when stimulated by incident light. Studies of the isolated iris of the eel
have shown that the action spectrum for contraction has a major peak
at 600 mp, and resembles the absorption spectrum for eel rhodopsin
(Seliger, 1962).
C . The Tapetunb Lucidurn of Chondrichthyea
There is a niirror or tapetum lucidum (L. tapete, carpet) in the eye
of chondriohthian fishes, which is responsible for the remarbble eyeshine that they exhibit. Eyezdhine, of course, is most evident in those
species whose pupils remain open when illuminated and in bathypelagic
species with large pupils. The tapetum lucidum contains reflecting cells
that lie in the inner layer of the chorioid, immediately underneath the
ohoriocapillaris (Fig. 2). It is present in most elasmobranch and it
also occurs in holocephalans (Franz, 1905 ; Walls, 1942). It appears to
be absent in the bathybenthic torpedo Benthobat& with rudimentary
eyes ; at least one is not mentioned by Brauer (1908). A tapetum is said
to be lacking in Laemargua (=Somniosw, an abyssal shark), aayliobatM