1+00 EXPERIMENTAL FISH EMBRYOLOGY 



DRAWING OF GERM RING AND KEEL EXCISION EXPERIMENTS 



C, ABLATION EXPERIMENTS ON LATER STAGES : (stages #20 to #25 all decapsulated. ) 



1. Remove the pectoral fin as it appears as an anlage' posterior and ventral to 

 the ear vesicle (stage #20). 



2. Remove the eye from one side only. This may be accomplished by drawing the 

 eye Into a small-bore pipette and then cutting it off at the base with a 

 fine needle knife. 



5. Remove the otic vesicle (stage #20). With controlled oral suction the ear 

 vesicle can be removed without injury to the adjacent medulla, but there is 

 generally no regeneration and the embryo later shows circus movements In 

 consequence. 



k. Remove small parts of the nerve cord (stages #17 to #20). This may also be 

 done by auction, but it is difficult to limit the amount removed. Not more 

 than the equivalent of 2 somite lengths should be removed, and a minimum of 

 the adjacent notochord and lateral mesoderm. 



5. -Remove parts of the brain, also by the suction method. This operation seema 

 to be less drastic for the embryo than some of the others, but it is some- 

 what more difficult to localize the ablation. No two embryos will be iden- 

 tically treated, hence Individual records are required. 



