288 CHARLES R. STOCKARD 



SUMMARY 



1 . Experiments in which certain regions are removed by mechan- 

 ical operations from the medullary plate of Ambly stoma punctatum 

 seem to show that the earliest optic anlage is median in position. 



Thirty embryos from which lateral portions of the medullary 

 plate and the anterior lateral part of the medullary fold were 

 removed at slightly different stages gave in twenty-four cases, 

 or in 80 per cent of the individuals, subsequent development of 

 both eyes. In five individuals one eye was absent and in one 

 specimen both eyes failed to arise. The absence of eyes in the 

 latter cases was probably due to the cut having been made in a 

 more median position than was intended. 



Nine individuals were operated upon so as to remove narrow 

 strips of cells from the anterior median portion of the medullary 

 plate. Four of these cases, or about 45 per cent of the specimens, 

 failed entirely to develop eyes. According to Spemann and 

 others they should have given some degree of cyclopia. Four 

 other individuals possessed highly defective Qyes, one embryo 

 having one eye poorly formed while the other was questionably 

 present. Only one of the nine specimens so operated upon was 

 capable of developing both eyes to an extent approaching the 

 normal. 



2. When the cells in the anterior portion of the open medullary 

 plate are disturbed by being stuck and scraped in various ways 

 with steel needles they do not loose their power of giving rise 

 to optic vesicles and cups which are normal in appearance during 

 the early stages, later stages were not studied. 



3. If the optic anlage be cut out of the medullary plate and re- 

 versed in position and then transplanted in the medullary plate 

 it still retains the power to give rise to optic vesicles and cups 

 which are abnormal in position to an extent depending upon the 

 distance the anlagen were shifted by the operation. 



The facts furnished by these experiments are considered in 

 connection with recent views regarding the genesis of certain 

 ophthalmic defects. 



