252 Origin and Differentiation of the Lens 
mediate effects of the operation, but retardation results only later from 
the lack of influence of the optic cup. In other words, after removal of 
the optic vesicle, lens development still continues for a short time, the 
extent of the development depending upon the size of the lens-plate at 
the time of the operation. The lens seems to receive a sort of momen- 
tum from the contact influence of the optic vesicle, and this impulse or 
stimulus is sufficient to give the lens a limited amount of self-differen- 
tiation, even in the absence of the optic cup. In all cases where long 
enough time is allowed, the process of separation of the lens from the 
ectoderm takes place, although generally the lenses lie nearer to the ecto- 
derm after their separation than the normal ones. 
Three other embryos (Experiments IX,,4.4,) of this stage (IX), 
which were killed six, eight, and thirty days after the operation, show 
slight regeneration of the right eyes. In the six-day embryo, the right 
lens contains a mass of fibers surrounded by a complete layer of epi- 
thelium, and no medial pole is distinguishable. In the other two in- 
stances the regeneration of the eye was very slight, and the lenses are 
not only considerably retarded in growth, but also in differentiation. In 
the 30-day embryo the difference in size of the two lenses is 120 p, the 
left measuring 260 and the right only 140 in diameter. The latter 
contains some fibers and material staining like the normal lens. This 
material seems to be degenerated lens-fibers. Owing to slight regenera- 
tion of a few optic vesicle cells, the lens was perhaps at first rather 
normally developed and differentiated, but these few cells were not 
sufficient to influence the lens completely, and hence after a short time 
degeneration occurred. 
In the next stage (X) the gill mass is large but shows no division. 
The lens-bud is well marked when the skin flap is turned forward in the 
operation (Figs. 15-16). 
In one embryo (Experiment X,,) that was allowed to live 14 days 
after the operation the normal lens measures 160 and the right one 
100 » in diameter, thus showing a difference of 60 » in size. The right 
lens has separated from the ectoderm but the eye is entirely wanting. 
A complete layer of epithelium surrounds the lens, which contains be- 
sides degenerated material a few healthy fibers in the region that had 
once been the medial pole (Fig 17, and compare Fig. 27). 
In three other experiments (X,, 55.4), 11 which the embryos were 
allowed to live seven, nine, and eleven days, slight regeneration of the 
right eyes has taken place. In the seven-day experiment the regenera- 
tion is very slight indeed. The right lens is fairly normal in appear- 
ance, but somewhat retarded (Figs. 18-19). It has separated from 
