412 Charles R. Stockard. 
5 DISCUSSION OF PREVIOUS OBSERVATIONS AND EXPERIMENTS 
Before drawing final conclusions from the cases discussed above 
it may be well briefly to review the modern work and experi- 
ments which have been directed towards a solution of the so- 
called lens problem. 
Rabl (’98) in his study of the structure and development of the 
lens, found in one case, at least, that a lens-like body was present, 
although far removed from the optic vesicle. This observation 
has been criticised by Lewis, who suggested that the ectoderm 
with the newly forming lens had shifted away from the small 
optic vesicle. Again, Lewis states that Rabl’s case, and also a 
case to be considered below that was shown by Mencl, prove 
neither one side nor the other, since the experimental evidence 
is all directly for the idea that a lens will not arise from the skin 
without the stimulus of the optic vesicle. At the present time, 
however, the experimental evidence points in an opposite direc- 
tion, and the cases of Rabl and Mencl can scarcely be disposed 
of in so brief a manner. On the contrary Rabl’s example must 
be considered the initial illustration of the origin of an early 
lens without a stimulation from the optic vesicle. 
Following this single case a strong tide turned towards the 
idea of the dependent origin and development of the optic lens. 
Herbst’s paper (’01) on ‘‘Die formative Reize in der thierischen 
Ontogenese’’ and Spemann’s pioneer experiments (’01) on the de- 
velopment of the lens seemed most convincing evidence in favor of 
a correlation in development between the optic vesicle and the 
lens, a correlation in which the latter played a dependent réle. 
Herbst claimed the optic lens to be a ‘‘Thigmomorphose”’ origi- 
nating only by a contact between the optic vesicle and the epi- 
dermis. His reason for such a position being that in the case 
of cyclopean monsters the median optic vesicle always derives 
a lens from the overlying ectoderm, while no lenses arise in the 
usual lateral positions. “If the lens is an independent organ why 
does it not arise in the lateral eye region of cyclopean monsters?” 
In former experiments the writer (09) produced just such a case 
as Herbst thought necessary to show the independent origin of 
@ 
