420) Charles R. Stockard. 
2 The crystalline lens may originate from ectoderm without 
any direct stimulus whatever from an optic vesicle or cup. These 
self-originating lenses arise from regtons of ectoderm that are 
not in contact with either optic vesicle, the brain wall, or any 
nervous or sensory organ of the individual (see plate I). 
3 The lens-plate or lens-bud is capable of perfect self-differen- 
tiation. No contact at any time with an optic vesicle or cup, 
is necessary. These lenses finally become typical transparent 
refractive bodies exactly similar in histological structure to that 
in the normal eye (see plate IT). 
4 The size and shape of the lens is not entirely controlled by 
the associated optic cup. Lenses may be abnormally small for 
the size of the cup, or entirely too large, so that they protrude; 
or, finally, peculiarly shaped oval or centrally constricted lenses 
may occur in more or less ordinarily shaped optic cups. The lens 
is by no means always adjusted to the structure of the optic cup 
as has been claimed by some observers. 
5 An optic vesicle or cup is invariably capable at some stage 
of its development of stimulating the formation of a lens from 
the ectoderm with which it comes in contact. It is remarkable 
how extremely small an amount of optic tissue is capable of stimu- 
lating lens formation from the ectoderm (plate II, fig. 5). 
6 The optic vesicle may stimulate a lens to form from regions 
of the ectederm other than that which usually forms a lens. This 
is shown by the fact that a median cyclopean eye always stimu- 
lates a lens to form from the overlying ectoderm. It is scarcely 
possible that the lateral normal lens-forming ectoderm could 
follow the cyclopean opti¢ cup to the many strange situations 
it finally reaches. 
7 The ectoderm of the head region is more disposed to the 
formation of lenses than that of other parts of the body, since the 
free lenses invariably occur in this region. 
8 <A deeply buried optic vesicle or cup may fail to come in 
contact with the ectoderm; in such cases it lacks a lens. The 
tissues of the embryonic cup itself are unable to form or regenerate 
alens. This is not true in all embryos, as Lewis has shown for 
one species of frog. 
