Wilbur L. Le Cron 257 
tion. Is the medial pole, destined for the formation of the lens-fibers, 
predetermined for a definite part of the developing lens, or can the pole 
be formed at any part of the circumference by modifying the surrounding 
influences at an early stage? Many interesting questions suggest them- 
selves, some of which can be determined by experiment, while for others 
only hypotheses at present seem possible. 
What the nature of this continued contact influence exerted upon the 
lens may be, is purely hypothetical. Perhaps, substances chemically 
formed in the protoplasm of the optic cup cells may be the important 
factors, which in some way are able to change the chemical nature of 
the lens cells, and thus promote their development into a normally dif- 
ferentiated lens. In the early stages of lens formation, the optic vesicle 
is in close contact with the developing lens, and there may be some 
kind of a protoplasmic connection, a relation of the two tissues, such 
that there may occur an interchange of protoplasm, or, what is more 
hkely, of substances chemically formed in the protoplasm. This influ- 
ence of the adjacent optic vesicle or optic cup, whatever may be the 
manner of its production, being chemical in nature or otherwise, proba- 
bly continues throughout lens development and differentiation, and per- 
haps is even exerted to a certain degree upon the lens of the adult eye. 
However, the conditions of the lens in the older embryos are such that 
the effects of removal of the optic cup are only felt after some days. 
It is evident, then, that the age of the embryo indicates somewhat the 
extent of the effect produced by the removal of the optic vesicle. The 
lens may continue to grow some, even after disturbing these normal re- 
lations with the optic cup, but its growth is inevitably checked and is 
especially abnormal with regard to differentiation, due, undoubtedly, to 
the loss of influence, whatever its nature may be, of the optic cup. 
CONCLUSIONS. 
(1) A lens will not arise from the normal lens-forming area of the 
ectoderm without the contact influence of the optic vesicle. The lens 
is not self-originating. 
(2) A lens will not develop from the lens-plate, lens-bud, or lens- 
vesicle, when the optic cup is removed. The lens is not self-differ- 
entiating, but is dependent upon the continued influence of the optic 
cup for its normal development. 
(3) The older the lens rudiment at the time of removal of the optic 
cup, the greater the amount of independent differentiation the lens rudi- 
ment possesses. - 
(4) The lens rudiment ultimately ceases to develop after removal of 
the optic cup, and finally degenerates. 
