POSITION OF OPTIC ANLAGE IN AMBLYSTOMA 265 



median position in the medullary plate or groo\'e. I have been 

 led to think from a study of a number of eye abnormalities that 

 the eye anlage is more or less median in its original position. 



6. The removal of anterior median strips of cells from the wide 



medullary plate 



Tn these operations a narrow median strip was cut from the 

 anterior region of the wide medullary plate. The strip in all 

 cases was narrow, being in fact only about one-third or one-fourth 

 the entire width of that portion of the medullary plate lying be- 

 tween the medullary ridges, as shown in figure 5. 



Four embryos with wide medullary plates were operated upon 

 in the above manner. Four days later they were preserved for 

 study. 



Three of these four specimens were eyeless, showing that the 

 operation had removed the entire eye anlage from the middle 

 of the medullary plate. The remaining one of the four embryos 

 had one poorly formed eye while the other was only slightly 

 indicated, so that in this case almost all of the ability to develop 

 eyes had been lost as a result of the operation. 



Five other embryos were subjected to a similar operation to 

 that indicated in figure 5 except that the median strip removed 

 was still narrower than in the preceding experiment. These 

 embryos were of different stages but all showed the medullary 

 folds far apart so that the medullary groove was wide open. 

 Three days after the operation the embryos were prepared and 

 studied. 



One of the specimens was eyeless, one had two poorly devel- 

 oped eyes, two had one well formed eye while the other eye was 

 questionable or absent, one had both eyes present. Thus the 

 removal of a very narrow median strip gave less decided effects 

 than the removal of somewhat wider strips in the experiment 

 above. Yet four out of the five embryos showed eye defects, 

 two having both eyes affected and two having one normal eye 

 and one eye questionable or absent. 



