Experimental Studies on the Development of the Eye. 439 



MF,.) The contracted cup with small cavity and pupil pre- 

 sents a similar appearance to the condition seen in Experiment 

 MD4. The extent of the endothelium and of the cornea cor- 

 respond in size with the cup. The cornea is somewhat thicker 

 than the normal one on the opposite side of the head, but other- 

 wise similar to it. 



I have numerous other similar experiments giving like results. 

 In these experiments the optic cup or its endothelial membrane 

 lie close to the corneal clearing, which corresponds in size with 

 the area of contact. If, however, the optic cup and its endo- 

 thelial membrane lie somewhat deeply buried and separated 

 from the ectoderm by mesenchyme the corneal clearing fails to 

 develop. 



The formation of the cornea is then neither dependent upon the 

 formation of a lens nor upon the presence ot the lens. 



E. Small Corneal Clearing over the Superficial Naked Lens. 



If in Amblystoma the optic cup is taken out about the time of, 

 or shortly after, the separation of the lens from the skin and the 

 lens left in position close against the skin, a small clear corneal 

 area will develop immediately over the naked lens. In such 

 experiments there was at the time of the operation no trace of 

 cornea and if both optic cup and lens are taken out the small 

 area of corneal clearing does not appear. 



An incision was made about the caudal two-thirds of the eye 

 and the whole eye and skin-flap turned forward together. The 

 optic cup was then carefully removed, leaving the lens in situ and 

 the skin-flap with the lens attached turned back into its normal 

 position. 



At about the time when corneal clearing appears on the normal 

 side the skin over the lens clears also, but is limited to the area 

 immediately over the lens. As both epidermis and lens become 

 perfectly transparent one can look down into the depths of the 

 head in the living animal. The lens in most of the embryos is 

 considerably smaller than the one on the normal side and often 

 shows degeneration changes. The endothelial layer does not 

 develop about the naked lens. The corneal area does not seem 

 to spread beyond the extent of the contact area of the lens, nor 



