Wilbur L. Le Cron 247 
The optic vesicle is in contact with the ectoderm, but is not adherent to 
it (see Fig. 2). 
Five embryos (Experiments VII,, 75 2s 35 32) of this stage (VII) thus 
operated upon and killed 2, 4, 9, 10 and 12 days later, show no regenera- 
tion of the right eyes and-likewise no signs of lens formation. In two 
embryos killed seven and nine days after the operation there appear 
partially regenerated eyes, which, owing to their small size and lack of 
contact with the overlying ectoderm, have failed to stimulate lens forma- 
tion. Other embryos (Experiments VII,,,,7; ) operated upon and al- 
lowed to live five, seven, and two, eight days, show regenerated eyes 
with developing lenses. In these the regenerated eyes were of sufficient 
size to come into contact or to remain in contact with the ectoderm long 
enough to cause lens formation. These latter experiments thus indicate 
that the operation of turning back the skin flap does not interfere with 
lens development, provided that the flap, when returned to its original 
position, comes into contact finally with a regenerated optic vesicle. 
On the left or normal side of the embryo referred to above, which was 
killed two days after the operation, there is still no trace of the lens- 
plate, but on the normal side of the one killed four days afterwards, the 
lens-bud is well advanced, and in the embryos allowed to live five days, 
the lens-buds are still attached to the inner layer of the ectoderm and 
are about 110 microns in diameter. Embryos killed eight and nine days 
after the operation, however, show that the normal lens has completely 
pinched off from the ectoderm, and that the lens-fibers are beginning to 
differentiate at the medial pole. At eight days the lens is about 140 p 
in diameter. The normal lens in the embryo allowed to live 10 days is 
about 130) in diameter and has pinched off from the ectoderm, and 
lens-fibers are fairly well developed. The normal 12 day lens is about 
150 » in diameter and shows still further differentiation. 
The contrast, then, between no lens at all on the right side, where the 
optic vesicle is small or wanting even 12 days after the operation, and 
the normal lens on the left side is very marked indeed, and leads to the 
conclusion that the lens in Amblystoma as in Rana is not a self-originat- 
ing structure. 
In one embryo (Experiment VII,,) which was allowed to live 30 days 
after the operation, the right eye is entirely wanting, but in the region in 
which the lens would have formed under normal conditions, there seems 
to be a lens-bud rudiment (see Fig. 3). Its small size and rudimentary 
condition is in marked contrast to the normal lens on the opposite side 
of the head (compare Fig. 9). This little lens-bud, if it is one, and this 
seems somewhat doubtful, has probably arisen because the embryo at 
the time of the operation had advanced, as regards the formation of the 
