8. VISION AND BIOLUMINESCENCE
243
(1888)) Chun (1896)) Giesbrecht (1896), Trojan (1907)) Pierantoni (1921))
and Bassot (1960a)b).
Pierantoni (1921) describes the development of the photophore in
the eye of Euphausia krohnii. It is noticeable in the eye of the first
calpytopis as a striated body present before the development of the
ommatidia (Fig. 85). Development is continuous and by the third
calyptopis the photophore is a recognizable organ. The layer of
reflecting pigment develops in the early furciliae (Fig. 85) and the
photophore is adult in appearance and functional in the later furciliae.
Heegaard (1948) points out that the thoracic and abdominal photophores are not recognizable, by eye, until the third furcilia although
rudimentary, unpigmented organs are sometimes present in the second
furcilia. The thoracic photophores begin to develop before the abdominal
photophores and similarly more anterior abdominal photophores
develop before more posterior ones. The eye photophore has no lens
(Fig. 85) whereas a lens is present in each of the thoracic and abdominal
organs (Fig. 86). A layer of reflecting pigment is present round the
back of the body photophores which, like the eye photophores, are
directed ventrally relative to the body of the animal. The reflecting
pigment, therefore, occludes light from the dorsal areas of the body and,
in the case of the eye stalk photophore, from the rest of the internal
tissues, including the light-sensitive rhabdoms of the eye. Each
abdominal photophore is located in the haemocoel ventral to, and
partially overlapped by, the respective segmental ganglion. Pour
strands, whose nature is unknown, attach each of the photophores to
connective tissue ligaments which lie alongside the subneural artery
(Hardy, 1964). These ligaments extend from a point anterior to the first
abdominal photophore to the region posterior to the fourth abdominal
photophore. They do not appear to be attached a t their posterior ends
but are attached a t their anterior ends to elastic connective tissue
fibres which originate from the anterior ventral edge of the first
abdominal segment. Two small muscles, one on either side of the first
photophore, originate from the ventral body wall and extend forwards
to connect to the anterior end of the ligaments. These muscles are
antagonistic to the elastic tissue fibres and are probably responsible for
the synchronous rotation of the abdominal photophores observed by
Hardy (1962).
Little is known about the histochemistry of euphausiid photophores.
Bassot (1 960a,b) has published electron micrographs of the photophores
of Meganyctiphanes norvegica and shows that the gland cells, located
between the striated body and the reflecting pigment layer, are of two
types. The first type is distributed round the edge of the striated body
243
(1888)) Chun (1896)) Giesbrecht (1896), Trojan (1907)) Pierantoni (1921))
and Bassot (1960a)b).
Pierantoni (1921) describes the development of the photophore in
the eye of Euphausia krohnii. It is noticeable in the eye of the first
calpytopis as a striated body present before the development of the
ommatidia (Fig. 85). Development is continuous and by the third
calyptopis the photophore is a recognizable organ. The layer of
reflecting pigment develops in the early furciliae (Fig. 85) and the
photophore is adult in appearance and functional in the later furciliae.
Heegaard (1948) points out that the thoracic and abdominal photophores are not recognizable, by eye, until the third furcilia although
rudimentary, unpigmented organs are sometimes present in the second
furcilia. The thoracic photophores begin to develop before the abdominal
photophores and similarly more anterior abdominal photophores
develop before more posterior ones. The eye photophore has no lens
(Fig. 85) whereas a lens is present in each of the thoracic and abdominal
organs (Fig. 86). A layer of reflecting pigment is present round the
back of the body photophores which, like the eye photophores, are
directed ventrally relative to the body of the animal. The reflecting
pigment, therefore, occludes light from the dorsal areas of the body and,
in the case of the eye stalk photophore, from the rest of the internal
tissues, including the light-sensitive rhabdoms of the eye. Each
abdominal photophore is located in the haemocoel ventral to, and
partially overlapped by, the respective segmental ganglion. Pour
strands, whose nature is unknown, attach each of the photophores to
connective tissue ligaments which lie alongside the subneural artery
(Hardy, 1964). These ligaments extend from a point anterior to the first
abdominal photophore to the region posterior to the fourth abdominal
photophore. They do not appear to be attached a t their posterior ends
but are attached a t their anterior ends to elastic connective tissue
fibres which originate from the anterior ventral edge of the first
abdominal segment. Two small muscles, one on either side of the first
photophore, originate from the ventral body wall and extend forwards
to connect to the anterior end of the ligaments. These muscles are
antagonistic to the elastic tissue fibres and are probably responsible for
the synchronous rotation of the abdominal photophores observed by
Hardy (1962).
Little is known about the histochemistry of euphausiid photophores.
Bassot (1 960a,b) has published electron micrographs of the photophores
of Meganyctiphanes norvegica and shows that the gland cells, located
between the striated body and the reflecting pigment layer, are of two
types. The first type is distributed round the edge of the striated body