VIII.
MORPHOGENESIS
OF THE VERTEBRATE EYE
347
eye coats (counteracting this stretching). Owing to this, at the site of the
formation of scleral cartilages around the corneal limbus, which slows
down the growth of the wall of the eye, the ciliary zone, which continues its growth, becomes folded, and its folds become arranged
radially, along the direction of the stretching forces of the eye cup wall.
Since intraocular pressure itself depends on the function of the ciliary
body it seems that their interrelation, when either is disturbed, must
lead to progressive inhibition of eye growth, and therefore to defects of
the eye as a whole.
No special works have been devoted to the causal relations in the
development of iris. Various incidental observations show a relation
between its formation and intraocular pressure and the contact between
the iris and the lens. In amphibian larvae lacking a blood circulation
(Kemp, 1953; Kemp and Quinn, 1954; Lopashov, 1960), no vitreous
chamber is formed, and the iris is wanting. Though the iris in amphibians
can start its formation without the lens, if the eye rudiment preserves
its connection with the ectoderm (Lehmann, 1934, 1936; Reyer, 1950),
the lens seems nevertheless to play a certain role in iris differentiation.
Giroud (1957) and Stroeva (1960) showed that iris differentiation in rats
is restricted to the zone of contact between the eye cup margin and the
lens. The mechanism of iris formation remains a task to be solved by
special investigations.
IV. Induction of the Lens
The lens rudiment is formed where the eye rudiment comes into
contact with the ectoderm. Arising in the form of an ectodermal
thickening, the lens rudiment closely adjoins the bottom of the cup, and
then separates both from it and from the ectoderm, preserving a connection with the pupillary margin. The close connection of the lens rudiment with that of the eye long ago suggested a causal relation in their
development. This led to the finding of the dependence of lens appearance on the action of the eye rudiment on the ectoderm (Spemann, 1901,
1905; Lewis, 1904, 1907), to which attention was drawn for a long time
in investigations of the mechanism of eye development.
This was a controversial question from the very beginning. Along
with the formation of the lens in dependence on the eye rudiment and
the absence of lens after the removal of the eye rudiment found in most
species, in some others such as Rana esculenta and Xenopus laevis
(Spemann, 1912; Balinsky, 1951) the lens was found to be formed even
after eye rudiment removal at neurula stage; in some other species, such
as Bombina pachypus, the lens can arise under the influence of the eye
anläge, but from the head ectoderm only (Spemann, 1912). When
MORPHOGENESIS
OF THE VERTEBRATE EYE
347
eye coats (counteracting this stretching). Owing to this, at the site of the
formation of scleral cartilages around the corneal limbus, which slows
down the growth of the wall of the eye, the ciliary zone, which continues its growth, becomes folded, and its folds become arranged
radially, along the direction of the stretching forces of the eye cup wall.
Since intraocular pressure itself depends on the function of the ciliary
body it seems that their interrelation, when either is disturbed, must
lead to progressive inhibition of eye growth, and therefore to defects of
the eye as a whole.
No special works have been devoted to the causal relations in the
development of iris. Various incidental observations show a relation
between its formation and intraocular pressure and the contact between
the iris and the lens. In amphibian larvae lacking a blood circulation
(Kemp, 1953; Kemp and Quinn, 1954; Lopashov, 1960), no vitreous
chamber is formed, and the iris is wanting. Though the iris in amphibians
can start its formation without the lens, if the eye rudiment preserves
its connection with the ectoderm (Lehmann, 1934, 1936; Reyer, 1950),
the lens seems nevertheless to play a certain role in iris differentiation.
Giroud (1957) and Stroeva (1960) showed that iris differentiation in rats
is restricted to the zone of contact between the eye cup margin and the
lens. The mechanism of iris formation remains a task to be solved by
special investigations.
IV. Induction of the Lens
The lens rudiment is formed where the eye rudiment comes into
contact with the ectoderm. Arising in the form of an ectodermal
thickening, the lens rudiment closely adjoins the bottom of the cup, and
then separates both from it and from the ectoderm, preserving a connection with the pupillary margin. The close connection of the lens rudiment with that of the eye long ago suggested a causal relation in their
development. This led to the finding of the dependence of lens appearance on the action of the eye rudiment on the ectoderm (Spemann, 1901,
1905; Lewis, 1904, 1907), to which attention was drawn for a long time
in investigations of the mechanism of eye development.
This was a controversial question from the very beginning. Along
with the formation of the lens in dependence on the eye rudiment and
the absence of lens after the removal of the eye rudiment found in most
species, in some others such as Rana esculenta and Xenopus laevis
(Spemann, 1912; Balinsky, 1951) the lens was found to be formed even
after eye rudiment removal at neurula stage; in some other species, such
as Bombina pachypus, the lens can arise under the influence of the eye
anläge, but from the head ectoderm only (Spemann, 1912). When