394 Charles R. Stockard. 
exert over the development of the optic vesicle into the cup and 
its subsequent development into the eye? 
If it is proven that the optic vesicle and cup possess the power 
to derive a lens from the ectoderm the further question then 
arises is the ectoderm under any condition able to give rise to a 
lens without the optic vesicle stimulus? If so, is this independent 
lens-bud capable of self-differentiation to such an extent as to 
form a perfectly constructed lens? 
Many questions of detail, as, for example, the relationship 
between the size of the optic cup amd the size of the lens, the 
ability of partial or defective optic cups to stimulate lens forma- 
tion, whether the lens may be derived only from certain areas 
of ectoderm or from any ectoderm, and other problems which we 
will presently consider, also present themselves. 
The study of these questions has come to be known as the 
lens problem. Experimenters have attacked the questions from 
several sides during the last ten years and the lens problem has 
in many ways been beautifully analysed, yet today much addi- 
tional evidence is necessary to entirely clear the situation. 
In a previous paper the writer (’09) briefly described the inde- 
pendent origin and self-differentiation of the optic lens in the 
fish embryo. Since that time further experiments have yielded 
much additional material and evidence bearing on this subject. 
The results of these experiments are considered in the present 
contribution and show in a most convincing manner that the 
crystalline lens is capable of originating independently from the 
ectoderm and of subsequent self-differentiation. Definite proof 
will also show that although the lens may arise independently, 
nevertheless the optic vesicle invariably has the power to stimu- 
late the formation of a lens from any overlying ectoderm with 
which it may come in contact. 
The action of the optic vesicle on the ectoderm is a much 
stronger force for the production of a lens than is the innate 
tendency of the ectoderm to produceanindependentlens. Slightly 
injured ectoderm may be rendered unable to form a free lens 
while the same weakened ectoderm will respond to a contact 
