260 CHARLES R. STOCKARD 



slightly beyond the median line and certainly did not include 

 the left lateral medullary tissue. 



The other three embryos had both eyes present, though one 

 eye in one specimen and both eyes in another were abnormal or 

 defective. In these cases the cut did not extend close enough 

 to the median line to remove all of the eye substance of that 

 side; 3^et if the eye anlagen at this time had been lateral in posi- 

 tion, one would have been completely removed. 



A similar experiment was performed on seven somewhat earlier 

 embryos. In these cases where the medullary plate was younger 

 and wider in extent the removed area was confined to a lateral 

 position and did not extend close to the median line, yet it ex- 

 tended laterally into the medullary fold (fig. 2). 



Three days later the embryos were killed. On studying the 

 sections of the head region six of the seven embryos were found to 

 possess two perfect eyes of normal proportions. The seventh indi- 

 vidual had only one well defined eye while the other eye was 

 absent. 



The removal of this lateral area of tissue which has been con- 

 sidered the position of the early eye anlage by certain investi- 

 gators gives no effect on the development of the future eye unless 

 the cut be made to extend very close to the median line. In 

 eleven operations of this type nine individuals did not suffer the 

 loss of either eye, while one specimen lacked both eyes and 

 another one had only one eye. The case in which both eyes 

 were absent might have been due to the fact that the cut ex- 

 tended a little way beyond the median line and removed cells 

 destined to form the material of both eyes. Experiments re- 

 corded below would indicate that this was the case. A second 

 possibility is that the operation so weakened the individual — • 

 which may have been below normal in vigor, though apparently 

 perfect specimens were selected for all the operations — that it 

 lacked the power to differentiate the eyes from the medullary 

 tissue. 



Six of the nine specimens which possessed both eyes showed 

 no effects of the removed material in either the size or form of 

 their eyes. The other three embryos had one or both eyes some- 



