43^ Warre^i Harmo^i Leivis. 



usual vacuolization. It is in general like the normal corneal 

 ectoderm except in being somewhat thicker. The rudimentary 

 corneal area, however, never seems to become much larger than 

 that pictured in Fig. 2, even twenty days after the operation. 

 This experiment (Mn^) is only one of several in which almost 

 exactly similar results were obtained as regards the development 

 of the small corneal area. 



In most of these experiments the rudimentary cornea is at the 

 bottom of a depression in the ectoderm as in Experiment Mn^ 

 (Fig. 2). Such depressed areas occur, however, without corneal 

 changes. (See Fig. 3, Experiment MEj.) In this experiment 

 (ME2) the optic cup was removed some time before the separa- 

 tion of the lens from the ectoderm. The lens has been pinched 

 off from the skin and has become separated from the latter by 

 mesenchyme. The lens is, however, very much smaller than the 

 normal one on the other side of the head. The embryo was 

 killed 16 days after the operation and there is no trace of corneal 

 formation even at the bottom of the depressed ectodermal area. 

 The depression of the ectoderm then can scarcely be looked upon 

 as a factor in its clearing. 



In explanation of these rudimentary corneal areas it may be 

 that the influences causing corneal formation had, at the time of 

 the removal of the eye, not been acting long enough on the ecto- 

 derm to enable the clearing process to go on independently and 

 form the normal sized cornea. A longer continued influence of 

 the eye is evidently necessary for normal corneal formation and 

 as will be shown later on it is necessary for the eye to be present 

 even after the cornea is well formed if the latter is to continue its 

 existence. It may be that the cornea can never maintain itself 

 independently of the eye; however, farther experimentation is 

 necessary to determine this point. Here it again becomes apparent 

 that the cornea of normal size is not a self-differentiating structure. 



C. The Size of the Cornea is Dependent upon the Size of the Eye. 



In the various experiments where portions of the eye have been 

 cut away the regenerated eyes even thirty days after the operation 

 fail to reach the size of the one on the normal side, unless the 

 amount cut away is very small. The size of the regenerated 

 eye is somewhat in proportion to the amount of eye stuff left 



