Experimental Studies on the Development of the Eye. 441 



perfectly clear. And more than eight days may elapse before all 

 of the pigment cells are gone. 



In another experiment performed in a similar way (XVggg) 

 there was considerable disintegration of the eye before the new 

 skin completely covered over the denuded area. The eye is 

 about one-half the diameter of the normal one and the clear 

 corneal area even smaller in size. The various layers of the 

 retina are irregular and the lens also. The latter fills the pos- 

 terior chamber of the eye and has a process projecting into the 

 pupil. (Fig. II.) 



In these experiments as in those in which a portion of the 

 optic cup was cut away without injury to the overlying skin, the 

 size of the corneal area is in direct proportion to the area of 

 contact of the underlying eye. 



In these experiments the skin that grows over the eye is at 

 first opaque and shows no signs of clearing. Pigment cells are 

 scattered through it as in the ordinary epidermis. This con- 

 dition often remains until long after the cornea on the normal 

 side is well formed and clear. The clearing of the new epidermis 

 which has grown over the eye is usually a slow process, and a few 

 pigment cells are especially prone to remain even for a long time 

 after the skin has cleared. 



If not only the skin from over the eye is cut away but with it is 

 taken the lens and even the lens and part of the optic cup the 

 adjoining skin will slowly cover the optic cup and after consider- 

 able delay a cornea will form over this optic cup, the lens being 

 absent. The size of the cornea varies with the size of the 

 re-formed eye. Here, too, the corneal formation is much 

 retarded and only appears days after the one on the normal 

 side is well formed. 



If too much of the optic cup is taken away with the lens, what 

 remains may be so deeply buried that it does not come into con- 

 tact with the skin. In such embryos the cornea does not develop. 

 (See Fig. 12, from Experiment XVIIgjg.) 



If skin, lens, and optic cup are completely removed, new 

 epidermis will cover over the large wound but corneal changes fail 

 to appear even four weeks after the cornea has developed on the 

 normal side. So we can scarcely look upon the cornea in the 

 above experiments as a product of regeneration, but must con- 

 sider it as a new product from skin other than that which normally 

 gives rise to a cornea. 



