POSITION OF OPTIC ANLAGE IN AMBLYSTOMA 259 



indications of their misplacement. One individual showed one 

 abnormal eye while the other was probably indicated by a doubt- 

 ful eye structure situated within the archenteron. The general 

 structure of the eyes seemed normal and only slight indication 

 of their reversed origin was shown by a study of these early 

 stages. 



Thus if the eye anlage was contained within these cut-out 

 pieces the reversal and transplantation of the pieces did not 

 show any very detrimental effects on the future development of 

 the eyes, though in one of the eight cases one eye was abnormal 

 and the other was greatly misplaced and indistinctly indicated. 



The experiments of sticking and disturbing the cells in the 

 anterior end of the medullary plate without actually removing 

 the cells does not prevent the subsequent development of the 

 optic vesicles in an apparently normal manner. Cutting out 

 rectangular pieces of the medullary plate which contain the eye 

 anlage, reversing and replanting them merely cause the eyes to 

 develop in misplaced positions. These two experiments demon- 

 strate the fact that unless the future eye material is well re- 

 moved by the operation the optic vesicles may later form; this 

 is important in estimating the value of the results in the experi- 

 ments to follow. 



3. Lateral regions cut from the anterior part of the medullary -plate 



Four embryos were operated upon, as shown in figure 1. The 

 indicated region of the right lateral portion of the flat medullary 

 plate was cut entirely away with fine scissors. The area removed 

 did not extend quite to the median line except that in one case 

 it may have or probably did remove tissue beyond the median 

 line. The embryos were killed three days later, cut into sec- 

 tions and studied microscopically. 



One of the four lacked both eyes or had eyes so small and 

 poorly formed that they could not be recognized, and the brain 

 showed on one side indications of the operation. Both eyes had 

 thus been removed by an operation which extended at most 



