VIII.
MORPHOGENESIS OF THE VERTEBRATE
EYE
355
lens. In frogs, antigens are also revealed in the lens for the first time at
the placode stage (ten Cate and van Doorenmaalen, 1950). Newt lenses
formed by regeneration from the iris possess the same antigens as the
normal lenses of ectodermal origin (Titova, 1957; Langman and Prescott, 1959).
A different technique, investigating the effect of antibodies on the
developing lens, was used by Langman (Langman et al., 1957; Langman,
1959a). Presumptive lens ectoderm separated from the eye rudiment
before the onset of induction (before the 10 somite stage) grows in
culture in antilens serum. Its ability to grow decreases with age at
explanation and is completely lost at the 13-16 somite stage, but recovers again at the 16-18 somite stage. Correspondingly, no lens arises
in such cultures of lens ectoderm with the entire eye rudiment taken
before the 15 somite stage, and the lens-forming ectoderm undergoes
disintegration. Beginning with the 18 somite stage, the lens develops as
frequently as in control cultures. This method reveals that the substances capable of combining with antibodies to the lens arise in the
lens rudiment at the very onset of the induction. Finally, Woerdeman
(1953a, b) combined extracts of neurula ectoderm and eye vesicles of
axolotl and incubated them for 24 hours; he obtained positive reactions
of the extract to anti-lens sera which could not be obtained from
extracts of either of the original tissues alone. These interesting experiments show that lens antigens actually arise with the participation of
substances originating from both the ectoderm and the eye rudiment;
but they have not since been carried further.
All the data presented indicate that the lens arises by a sequence of
phases. The relation of the neural part of the eye to the lens has the
character of an inductive dependence, leading to the appearance of
qualitatively new cells at a definite time; after which the relationship is
continued but is of a different character. The dependence of extreme
sizes of the lens on the species peculiarities of the lens-forming ectoderm
(and not only on the dimensions of the eye rudiment) found by Rotmann
(1939, 1942) and especially by Balinsky (1957), shows a varying sensitivity of the ectoderm of different species to the action of the eye. But
these data do not imply that the action of the eye represents a stimulus
of a releasing character which brings about an innate reaction of the
ectoderm determined by its hereditary properties (Spemann, 1938;
Rotmann, 1939, 1942).
V. Mechanisms of Cornea Formation
The cornea is the external part of the optical system of the eye and, at
the same time, it serves to protect the main components of the eye from
MORPHOGENESIS OF THE VERTEBRATE
EYE
355
lens. In frogs, antigens are also revealed in the lens for the first time at
the placode stage (ten Cate and van Doorenmaalen, 1950). Newt lenses
formed by regeneration from the iris possess the same antigens as the
normal lenses of ectodermal origin (Titova, 1957; Langman and Prescott, 1959).
A different technique, investigating the effect of antibodies on the
developing lens, was used by Langman (Langman et al., 1957; Langman,
1959a). Presumptive lens ectoderm separated from the eye rudiment
before the onset of induction (before the 10 somite stage) grows in
culture in antilens serum. Its ability to grow decreases with age at
explanation and is completely lost at the 13-16 somite stage, but recovers again at the 16-18 somite stage. Correspondingly, no lens arises
in such cultures of lens ectoderm with the entire eye rudiment taken
before the 15 somite stage, and the lens-forming ectoderm undergoes
disintegration. Beginning with the 18 somite stage, the lens develops as
frequently as in control cultures. This method reveals that the substances capable of combining with antibodies to the lens arise in the
lens rudiment at the very onset of the induction. Finally, Woerdeman
(1953a, b) combined extracts of neurula ectoderm and eye vesicles of
axolotl and incubated them for 24 hours; he obtained positive reactions
of the extract to anti-lens sera which could not be obtained from
extracts of either of the original tissues alone. These interesting experiments show that lens antigens actually arise with the participation of
substances originating from both the ectoderm and the eye rudiment;
but they have not since been carried further.
All the data presented indicate that the lens arises by a sequence of
phases. The relation of the neural part of the eye to the lens has the
character of an inductive dependence, leading to the appearance of
qualitatively new cells at a definite time; after which the relationship is
continued but is of a different character. The dependence of extreme
sizes of the lens on the species peculiarities of the lens-forming ectoderm
(and not only on the dimensions of the eye rudiment) found by Rotmann
(1939, 1942) and especially by Balinsky (1957), shows a varying sensitivity of the ectoderm of different species to the action of the eye. But
these data do not imply that the action of the eye represents a stimulus
of a releasing character which brings about an innate reaction of the
ectoderm determined by its hereditary properties (Spemann, 1938;
Rotmann, 1939, 1942).
V. Mechanisms of Cornea Formation
The cornea is the external part of the optical system of the eye and, at
the same time, it serves to protect the main components of the eye from