21*8 



EXTIRPATION OF ORGAN ANLAGEN 



THE OPTIC VESICLE 



The optic vesicles of toth the Anura and the Urodela are capable of regulation. This 

 means that if the entire eye field is not removed, there may be a degree of restoration or 

 regeneration of the excised parts. No regeneration occurs when the entire optic vesicle 

 is removed, indicating that the eye-forming properties do not extend beyond the limits of 

 the prospective eye forming area. 



The above statements can be verified by removing only the outer retinal portion of 

 the optic vesicle In some embryos and the entire optic vesicle in others, examining by 

 dissection and by histological (sectioning) technique after a minimum of a week of recovery 

 and development at laboratory temperatures. 



The Anuran embryos at stage #17 (R> sylvatlca 

 and palustris preferable to plplens) or the Urodele 

 embryos at stage #25 or #26 may be used. Eemove 

 the membranes and place the embryo on its left 

 side in a Permoplast or agar depression in a Syra- 

 cuse dish. Locate the optic bulge and with a 

 glass needle and hair loop cut a rectangular piece 

 of epidermis directly over the eye, leaving the 

 upper margin of the rectangle uncut (a hinge). 

 Lift the flap of epidermis and locate the under- 

 lying optic vesicle. 



A. In some embryos, take the hair loop and cut 

 off the most lateral (outer portion) of the 

 optic vesicle, that portion known to give 

 rise to the retina. 



Extirpation of the retina and 

 the entire optic vesicle 

 Rana: stage #17. 



B. In other embryos, excavate the entire optic vealcle, clipping it off at its base. 



If the flap of epidermis is still intact, replace it over the wound. If it has been 

 damaged, simply leave the embryo in 10^ Standard Solution until the wound has closed com- 

 pletely by the spreading of adjacent epidermis, and then transfer to full strength Standard 

 Solution. The extirpation of the optic vesicle does not do away with the eye muscles 

 entirely but they are reducea In size and are atypical. 



Sketch (photograph) immediately 

 after extirpation 



Sketches (photographs) c 

 subsequent development 



