XII Proceedings of the Association of American Anatomists 
is it capable of self-differentiation or is the continued influence of the 
optic vesicle necessary for its normal development ? 
At the suggestion of Dr. Lewis, I undertook in the Spring of 1905 an 
experimental study of the question of self-differentiation of the lens in 
Amblystoma punctatum. It seemed possibie that by removing the optic 
vesicle, or optic cup, at various stages before and during lens formation, 
one would be able to determine whether continued influence of the optic 
vesicle is necessary for the perfect development of the lens. 
The operation of removing the optic vesicle without injury to the de- 
veloping lens or surrounding ectoderm is a simple one. The embryos 
were operated upon under the binocular miscroscope. A semicircular 
incision was made a little caudal to the eye region, and the skin flap 
turned forward, thus exposing the rounded optic vesicle. The latter 
was cut off close to the brain, and then readily removed, without injury 
to the lens-forming ectoderm or lens-bud. On replacing the skin flap 
into its original position, healing was rapid, requiring but a few hours. 
The embryos were killed in Zenker’s fiuid 2 hours to 30 days after the 
operation. In all 63 experiments were made. 
When the optic vesicle was removed from an embryo of a stage shortly 
after the closure of the neural folds, but before there were any signs of 
lens formation, the latter did not take place, unless the eye regenerated. 
In Amblystoma then, as in Rana, the lens is not a self-originating struc- 
ture. 
When the optic vesicle is removed during the time of formation of 
the lens-plate, the latter is found to possess very little power of self- 
differentiation and may remain as a mere thickening of the ectoderm. 
If the optic vesicle is removed at a later stage, when there is a well 
developed lens-bud, we find that it possesses more power of self-differen- 
tiation and will progress to the formation of a lens vesicle having walls 
one or two layers in thickness, but beyond this stage it does not seem to 
be able to differentiate, and even after many days, it remains in this con- 
dition, without the formation of lens-fibers. 
If the optic cup is removed at a still later stage, as when the lens 
vesicle has pinched off from the ectoderm, but still in contact with the 
same, we find that a still greater amount of self-differentiation is present, 
there being enough to carry the lens vesicle on at the normal rate for a 
few days, and lens-fibers will form. But its growth and differentiation 
ultimately become retarded and stopped, and certain changes set in. The 
lens-pole disappears, and new lens-fibers cease to originate, the anterior 
epithelial layer grows over this pole thus enclosing completely the lens- 
fibers, which begin to degenerate and finally become a mere vacuolated 
mass. 
