Independent Development of the Lens. 405 
wide double cup. In fig. 20 is seen a somewhat similar double 
cup with an elongated and slightly constricted lens; fig. 18 also 
shows one half of a double cyclopean eye with a double lens, 
the other half eye isin amore posterior section. In figs. 14 and 17, 
on the other hand, we find illustrated double lenses in one of 
two closely approximated eyes. Fig. 14 also shows a tiny addi- 
tional lens still further within the same cup which possesses the 
large double lens. Fig. 16 shows the extreme anterior tip of a 
cyclopean eye with two minute lenses protruding from it. This 
section is only fifty micromillimeters from the anterior end of the 
head. Numerous other examples of misfitting lenses might easily 
be given. 
These facts force us to conclude that the size of the optic cup 
does not fully regulate either the size or shape of the associated 
lens. It is, therefore, evident that the usual harmonious adjust- 
ment between the optic cup and the lens may not be so entirely 
due to a dominating influence of the optic cup on the lens as one 
might be led to believe from previous contributions to the sub- 
ject. That some influence or interaction exists; the writer does 
not deny, and will show in the following parts of this paper the 
remarkable ability possessed by the optic vesicle to obtain a lens 
from any part of the ectoderm with which it may come in contact. 
d Is the Optic Vesicle, Normal or Defective, always Capable of 
Stimulating Lens-Formation from the Ectoderm at Some Stage 
of its Development? 
Of all the embryos which the writer has examined not one failed 
to have a lens in a normal optic cup when the cup came in con- 
tact with the ectoderm. If, however, the cup fails to reach the 
outer body wall, although it may possess well differentiated reti- 
nal layers and other parts, it is invariably without a lens, fig. 26. 
The convex side of the choroid coat or pigment layer of the retina 
does not cause a lens to arise even though it be closely applied to 
the ectoderm, as is shown by fig. 26 and many other illustrations 
in which the choroid touches the body wall. 
Defective optic cups when deeply buried and separatea from 
