348
G. V. LOPASHOV AND O. G. STROEVA
asserting that these variants are 'dependent' or 'independent' development, not enough consideration was given to the fact that in the case of
independent development' one can mean only independence from the
eye rudiment and not independence from other actions.
Many works devoted to investigation of this initial contradiction are
of uncertain value. This is due to (a) heterogeneity of the type of experiment: removal of eye rudiments, transplantation of alien ectoderm
above the eye, transplantation of eyes under the ectoderm, explantation
of the lens-forming ectoderm—pure, with the eye rudiment, and with
other tissues of the head; (b) insufficient attention by some authors to
the necessity for complete removal of lens-forming cells and the carrying
out of control experiments, which has already been mentioned by Stone
and Dinnean (1940), and by Reyer (1950, 1954a, b). The aim of this
chapter will be to distinguish data contributing to the further solution of
the main problems, without describing in detail species differences the
demonstration of which is often doubtful.
Dependence of lens formation on the action of the eye was found,
besides in Amphibians, in Birds (chicks) (Alexander, 1937; van Deth,
1940; Amprino, 1949; McKeehan, 1954) and in Teleost fishes (pikes)
(Filatov, 1935), though in the latter group a number of cases of the
independent' development of lenses have been described. As was
shown by Filatov (1941, 1943), species differences in the dependence of
lens formation on the eye are related first of all to differences in the rate
of ectodermal ageing. The latter is a general phenomenon involving all
parts of the ectoderm as shown by Holtfreter (1938) and Gallera (1952).
At the stages preceding normal contact between the eye and the ectoderm, lens formation can be induced in the latter in all Amphibian
species. In experiments involving the wrapping of eye rudiments in
gastrula ectoderm (Brahma, 1959—Xenopus laevis), and transplantation under the ectoderm of the gastrula (Schmidt and Ragosina, 1937;
Lopashov, 1937—Triturus taeniatus; Woerdeman, 1938—Ambystoma
mexicanum; Sheina, 1940, 1944—Rana temporaria, R. arvális, R.
esculenta, Bombina bombina, Ambystoma mexicanum) lenses have
appeared in the majority of cases. This capacity is preserved in isolated
gastrula ectoderm up to the time when the control reaches the tail-bud
stage (Waddington, 1936; Brahma, 1959—Triturus alpestris, Xenopus
laervis). Finally, Sheina (1940, 1944) showed that the lens-forming
capacity of the ectoderm diminishes in different species at different
rates. Belly ectoderm of Rana temporaria, R. esculenta and R. arvalis at
the late gastrula stage forms lenses in 100% of cases, that of Bombina
bombina in 61%, that of Ambystoma mexicanum in 83-3%; at the neurula
stage lenses arise in R. arvalis in 42-9% only, while at the stage of the
closure of neural folds in R. esculenta in 19%, in R. arvalis in 36-4%, in
G. V. LOPASHOV AND O. G. STROEVA
asserting that these variants are 'dependent' or 'independent' development, not enough consideration was given to the fact that in the case of
independent development' one can mean only independence from the
eye rudiment and not independence from other actions.
Many works devoted to investigation of this initial contradiction are
of uncertain value. This is due to (a) heterogeneity of the type of experiment: removal of eye rudiments, transplantation of alien ectoderm
above the eye, transplantation of eyes under the ectoderm, explantation
of the lens-forming ectoderm—pure, with the eye rudiment, and with
other tissues of the head; (b) insufficient attention by some authors to
the necessity for complete removal of lens-forming cells and the carrying
out of control experiments, which has already been mentioned by Stone
and Dinnean (1940), and by Reyer (1950, 1954a, b). The aim of this
chapter will be to distinguish data contributing to the further solution of
the main problems, without describing in detail species differences the
demonstration of which is often doubtful.
Dependence of lens formation on the action of the eye was found,
besides in Amphibians, in Birds (chicks) (Alexander, 1937; van Deth,
1940; Amprino, 1949; McKeehan, 1954) and in Teleost fishes (pikes)
(Filatov, 1935), though in the latter group a number of cases of the
independent' development of lenses have been described. As was
shown by Filatov (1941, 1943), species differences in the dependence of
lens formation on the eye are related first of all to differences in the rate
of ectodermal ageing. The latter is a general phenomenon involving all
parts of the ectoderm as shown by Holtfreter (1938) and Gallera (1952).
At the stages preceding normal contact between the eye and the ectoderm, lens formation can be induced in the latter in all Amphibian
species. In experiments involving the wrapping of eye rudiments in
gastrula ectoderm (Brahma, 1959—Xenopus laevis), and transplantation under the ectoderm of the gastrula (Schmidt and Ragosina, 1937;
Lopashov, 1937—Triturus taeniatus; Woerdeman, 1938—Ambystoma
mexicanum; Sheina, 1940, 1944—Rana temporaria, R. arvális, R.
esculenta, Bombina bombina, Ambystoma mexicanum) lenses have
appeared in the majority of cases. This capacity is preserved in isolated
gastrula ectoderm up to the time when the control reaches the tail-bud
stage (Waddington, 1936; Brahma, 1959—Triturus alpestris, Xenopus
laervis). Finally, Sheina (1940, 1944) showed that the lens-forming
capacity of the ectoderm diminishes in different species at different
rates. Belly ectoderm of Rana temporaria, R. esculenta and R. arvalis at
the late gastrula stage forms lenses in 100% of cases, that of Bombina
bombina in 61%, that of Ambystoma mexicanum in 83-3%; at the neurula
stage lenses arise in R. arvalis in 42-9% only, while at the stage of the
closure of neural folds in R. esculenta in 19%, in R. arvalis in 36-4%, in