286 



EYE FIELD OPERATIONS 



d. Remove ectoderm and substrate (mesentoderm) froni area "C". 



e. Remove the entire area "A - C - B", ectoderm only. 



f. Remove the entire area "A - C - B", ectoderm and substrate (mesento- 

 derm). 



Camera-lucida drawing of a section through the prechordal region of 

 an Amblystoma neunila (Harrison stage #15). The mesoderm has just 

 begun to separate from the lateral portion of the roof of the archen- 

 teron. This gives an idea as to the distribution of the (mesentoderm) 

 substrate referred to in the excision experiments. 



Drawing from Adelmann 1930; Jour. Exp. Zool. 57:223. 



Anura* (stage #16 or #17) or Urodela (stage #21 to #25) 



a. Remove the ectoderm only from over the right optic vesicle. 



b. Remove the ectoderm and the optic vesicle from the right side. 



Diagram, showing in stipple the area which it is necessary to 

 remove in order to prevent completely the formation of an 

 eye on the operated side. 



From Adelmann 1929: Jour. Exp. Zool. 54:249 



c. Insert a sharp operating (glass) needle, beneath the ectoderm and, with 

 an up-lifting movement, cut the ectoderm along the dorsal, posterior, 

 and ventral margins of a rectangular area which includes the entire eye 

 field. This will provide a flap of ectoderm, with an anterior hinge. De- 

 flect this flap forward, and with a stiff hair loop, scoop out the entire 

 optic vesicle from beneath. Replace the ectodermal flap and allow it to 

 heal in place. If the excavation is so extensive that there is no base upon 

 which the ectoderm can lie, fill in the hole with yolk from another embryo. 



B. Cauterization : 



Using a heated and slightly bent needle, attempt to cauterize the entire optic- 

 ocular primordia on one side, as indicated in the accompanying diagrams. It 

 may be necessary to dip the needle into glycerine to prevent the hot needle from 

 drawing out some of the cellular contents of the neurula. The entire anlage' may 

 be found both within and without the medullary plate area. This is a delicate 

 operation and there will be high mortality, but the results (if the operation is 

 properly executed) will be very significant. 



When the embryos have reached the external gill stage, fix them in 10% formaldehyde and 

 dissect out the optico-ocular apparatus to compare it with the controls. During the heal- 

 ing and early development of the excised areas, macroscopic examinations and records 

 should be made. (See Glossary on "Double Assurance". This does not hold for Rana 

 sylvatica, Rana palustris, Rana catesbiana or Amblystoma maculatum. ) 



* Rana sylvatica or Rana palustris are better for this than is Rana pipiens. 



