266 CHARLES R. STOCKARD 



Combining the results of the two experiments it is found that 

 the removal of narrow median strips from wide medullary plates 

 exerts the following influence on the future development of the 

 eyes: Of nine embryos thus operated upon four failed entirely to 

 develop either eye. Two showed two defective eyes. Tivo individ- 

 uals developed one perfect and one defective or questionable eye. 

 Only one of the nine embryos showed two apparently normal eyes. 



Since six of the nine embryos had the development of both 

 eyes either entirely suppressed or decidedly affected, and two of 

 the remaining three had one eye affected, it seems most certain 

 that cells destined to take part in eye formation are located in 

 the median region of the medullary plate and are removed by 

 the operation employed. One must conclude that the median 

 optic anlage occupied at least one-fourth or one-third of the 

 width of the medullary plate in the anterior region. 



A general statement of the results of certain of the experi- 

 ments described above may be expressed as follows: Thirty em- 

 bryos studied after various operations in which lateral portions 

 of the medullary plate were removed at slightly different devel- 

 opmental stages (sections 3, 4, 5) showed in twenty-four indi- 

 viduals, or 80 per cent of the cases, subsequent development of 

 both eyes, while only six specimens or 20 per cent of the cases, 

 showed absence of the eye. In one case the presence of the eye 

 is questionable, in five cases one eye and in one case both eyes 

 were absent. The absence of eyes in the latter cases is possibly 

 due to the cut having been made in a more median position than 

 was intended. 



Nine embryos studied after having been operated upon so 

 as to remove a narrow median strip of cells from the anterior 

 portion of the medullary plate (section 6) showed in four cases, 

 or about 45 per cent of the specimens, entire absence of eyes. 

 In four other individuals the eyes were highly defective, one 

 specimen having one poorly formed eye while the other was 

 questionably present. In only one of the nine embryos did both 

 eyes approach the normal condition, from this specimen an ex- 

 tremely narrow piece had been cut away. The optic anlage in 

 this case might have been sufficiently wide at the time of the 



