EYE FIELD OPERATIONS 



295 



b. Bemove ectoderm and autatrate ( mesentoderm) from the same area ("A" or 

 "B") of another neurula. 



c. Bemove ectoderm only from area "C". 



d. Bemove ectoderm and auhstrate { meaentoderm) from area "C". 



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



f. Bemove the entire area "A - C - B", ectoderm and suhstrate (meaento- 

 derm) . 



Anura* (atage #l6 or #1?) or Urodela (stage #21 to #25) 



a. Bemove the ectoderm only from over the right optic vealcle. 

 h. Bemove 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 complete- 

 ly the formation of an eye on the operated side. 



From Adelmann I929 : Jour. Exp. Zool. 5l+:2i<-9 



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

 with an up-lifting movement, cut the ectoderm along the dorsal, pos- 

 terior, and ventral margins of a rectangular .area which includes the 

 entire eye field. This will provide a flap of ectoderm, with an 

 anterior hing?. Deflect this flap forward, and with a stiff hair 

 loop, scoop out the entire optic vesicle from beneath. Beplace 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. CAUTEBIZATION : 



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

 optic-ocular prlmordia 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 embiyos have reached the external gill atage, fix them in 10^ formaldehyde 

 and diasect out the optico-ocular apparatus to compare It with the controls. During the 

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

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

 aylvatica, Bana palustris, Bana catesblana or Amblystoma maculatum. ) 



SELF-DIFFERENTIATION OF THE EYE ANLAGE 



Consult the exercise on "The Culturlng of Isolated Amphibian Anlage" for the descrip- 

 tion of the basic procedure necessaiy for this part of the exercise. 



Isolate and attempt to culture the same areas used in the "Defect Experiments" 

 ( above) . 



The degree of self -differentiation is indicated by the degree of independent develop- 

 ment in isolation culture. This part of the exercise should Inform the student as to Just 

 when the lens and the vesicle (retina, etc.) are "self-differentiated". 



* Bana aylvatica or Bana palustria are better for this than is Bana pipiens. 



