262 CHARLES R. STOCKARD 



what smaller than usual. The cases with only one eye defective 

 are perhaps clearly understood on the ground that the cut en- 

 croached upon the material destined to take part in the devel- 

 opment of this eye. In the cases with both e3^es defective it 

 scarcely seems possible that the opposite eye could have been 

 injured by these cuts without entirely removing the eye on the 

 side where the cut was so extensive. The only plausible possi- 

 bility is that the material for both eyes was mediallj^ located and 

 the two eye anlagen closely connected. Any injury to this region 

 might later be shown by both eyes if the injury were at all exten- 

 sive, and if less extensive and confined entirely to one side of 

 the median line only one eye might show the effect. 



I realize that this explanation might be interpreted in part 

 as opposed to Spemann's experuuents in which he found the 

 future eye materials so consistently definite in the medullary 

 plate. When the eye anlage was cut transversely and the pos- 

 terior portion reversed and planted in a distant position it was 

 found that if the forward part of one eye was small the part 

 which had been cut from this and placed posteriorly was large. 

 This fact does not indicate entirely that the eye stuffs are sepa- 

 rate; only that when the eye anlage, even if it be median and 

 single, is cut across obliquely and the posterior part removed 

 and transplanted it continues development in a normal consis- 

 tent manner, the small eye part coming off on the side where 

 less material exists and vice versa. 



4. The anterior lateral part of the 7ieural fold and a portion of the 

 medullary wall cut from one side 



These experiments were performed on embryos older than those 

 used above in order to test whether the eye anlagen shortly 

 before the coming together of the neural folds might be situated 

 laterally along the border of the folds. In other words, do the 

 eye anlagen primarily arise in the median line or region of the 

 medullary plate and later occupy more lateral positions? 



The operation consisted in cutting away one side of the ante- 

 rior part of the medullary fold and also including in the removed 



