VIII.
MORPHOGENESIS OF THE VERTEBRATE EYE
365
the onset of chondrification the percentage of mitoses falls more rapidly
than in unoperated eyes. Experiments on the incorporation of radioactive sulphur showed, however, that, though the absolute amount of
cartilage in operated eyes is strongly reduced, this reduction does not
affect the synthesis of chondroitinsulphuric acid (Amprino and Pansa,
1955). Thus decrease of intraocular pressure removes all the mechanical
conditions of scleral stretching which bring about its intensive growth;
not the internal but the appositional growth of the sclera is then
reduced (Weiss and Amprino, 1940; Amprino and Pansa, 1955).
There seems to exist some correlation between the formation of the
choroid coat and of the sclera, since colobomas of both of them are
always accompanied by either a lack or a marked decrease in thickness
of the sclera in these areas (Mann, 1957; Gayer, 1942; Giroud et al.,
1954; Giroud, 1957). Our knowledge of the formation of the mesenchymal envelopes of the eye is however in general very poor and further
investigations are needed.
VII. Morphogenesis of the Eye and Some
General Problems of Embryology
The eye can serve as a kind of model object for the understanding of
some general problems of embryology. It is made up of rudiments of
different origin, each of which has its own regularities of development
while all at the same time are causally related to each other. Each
successive step in the development of individual rudiments is from the
developmental phases of the other parts of the eye. Individual relations
can seem, in the presence of other ones, like single influences, of the type
of inductions, bringing about the whole course of subsequent events. As a
matter of fact, they represent complex connections of multiple interactions which lead to either a promotion or an inhibition of individual
phenomena in the parts of the developing eye rudiment. These processes
assume a most swift and definite course only in the presence of all the
phenomena involved in these relations, these phenomena being united
by their mutual enhancing or exclusion. This general mechanism leads
to the formation in a short time of a harmonious functional structure.
In order to understand all that has been done and that has to be
investigated in the development of the eye, and also the attempts to
identify more precisely the character of this complex mechanism
driving development, it is necessary to turn again to analysis and to
discuss the types of particular morphogenetic mechanisms participating
in the development of the eye.
The morphogenesis of eye rudiments can be subdivided into several
periods during which morphogenetic mechanisms of different types are
MORPHOGENESIS OF THE VERTEBRATE EYE
365
the onset of chondrification the percentage of mitoses falls more rapidly
than in unoperated eyes. Experiments on the incorporation of radioactive sulphur showed, however, that, though the absolute amount of
cartilage in operated eyes is strongly reduced, this reduction does not
affect the synthesis of chondroitinsulphuric acid (Amprino and Pansa,
1955). Thus decrease of intraocular pressure removes all the mechanical
conditions of scleral stretching which bring about its intensive growth;
not the internal but the appositional growth of the sclera is then
reduced (Weiss and Amprino, 1940; Amprino and Pansa, 1955).
There seems to exist some correlation between the formation of the
choroid coat and of the sclera, since colobomas of both of them are
always accompanied by either a lack or a marked decrease in thickness
of the sclera in these areas (Mann, 1957; Gayer, 1942; Giroud et al.,
1954; Giroud, 1957). Our knowledge of the formation of the mesenchymal envelopes of the eye is however in general very poor and further
investigations are needed.
VII. Morphogenesis of the Eye and Some
General Problems of Embryology
The eye can serve as a kind of model object for the understanding of
some general problems of embryology. It is made up of rudiments of
different origin, each of which has its own regularities of development
while all at the same time are causally related to each other. Each
successive step in the development of individual rudiments is from the
developmental phases of the other parts of the eye. Individual relations
can seem, in the presence of other ones, like single influences, of the type
of inductions, bringing about the whole course of subsequent events. As a
matter of fact, they represent complex connections of multiple interactions which lead to either a promotion or an inhibition of individual
phenomena in the parts of the developing eye rudiment. These processes
assume a most swift and definite course only in the presence of all the
phenomena involved in these relations, these phenomena being united
by their mutual enhancing or exclusion. This general mechanism leads
to the formation in a short time of a harmonious functional structure.
In order to understand all that has been done and that has to be
investigated in the development of the eye, and also the attempts to
identify more precisely the character of this complex mechanism
driving development, it is necessary to turn again to analysis and to
discuss the types of particular morphogenetic mechanisms participating
in the development of the eye.
The morphogenesis of eye rudiments can be subdivided into several
periods during which morphogenetic mechanisms of different types are