Warren Harmon Lewis ANT 
With the point of a fine needle or a small pair of scissors the optic 
vesicle was cut off close to the brain, thus leaving a large opening into 
the ventricle. 
After removal of the optic vesicle the skin flap was returned into its 
original position and held in place for a few minutes either by the 
pressure of short pieces of silver wire, or better, by turning the embryo 
over, with the skin flap against the bottom of the dish, the weight of 
the embryo above being sufficient to hold the flap in place. There is 
often more or less contraction of the skin flap, so that it does not always 
cover the entire denuded ana. Healing takes place quite rapidly and 
in an hour or two the process is usually complete. The embryos were 
kept in small glass dishes and the water changed every day or two. 
The embryos were killed in Zenker’s fiuid at periods varying from 2 
to 20 days after the operation, embedded in paraffine, cut into serial 
sections 5 to 10 micro mm. in thickness and stained in hematoxylin and 
congo red. 
As great care was taken not to injure the skin flap, and especially 
that portion of the inner layer of the ectoderm which would, under 
normal conditions, have given rise to the lens, it seemed probable that 
the lens would arise unless it were in some way dependent for its origin 
directly or indirectly on the presence of the optic vesicle. It is easily 
shown that the mere turning forward of the skin flap from over the 
optic vesicle and then replacing it does not interfere with lens-formation, 
and even if a portion of the optic vesicle is cut away the remainder will 
regenerate an eye, and a lens will form from the ectoderm, provided, 
however, that the regenerated eye comes into contact with the ectoderm 
(see Figs. 67, 69, 71, 72, 73, 74, and 76). 
RESULTS FROM EXPERIMENTS. 
Absence of Lens-formation After Total Extirpation of the Optic Vesicle. 
In 50 of the embryos of rana sylvatica thus experimented upon and 
killed at from 3 to 16 days after complete extirpation of the optic 
vesicle, there was no regeneration of the eye and no indication of a 
lens or of lens-formation in the normal lens region from which the eye 
was taken. Fig. 4, from an embryo killed 3 days after complete extirpa- 
tion of the eye, shows complete absence of the eye and lens. Remnants 
of the optic stalk are imbedded in the ventral side of the brain. The 
normal eye on the opposite side of the head shows a large optic cup and 
lens (Fig. 5). Fig. 6 is from a section through the eye region of 
