388 



EXPERIMENTAL FISH EMBRYOLOGY 



Pass this pipette through the small aperture, and gently suck up a single blasto- 

 mere. This may require first the loosening of the blastomere with a slight cir- 

 cular movement of the pipette. If the pipette is attached by a small-bore rubber 

 tube held in the mouth the suction can be the better controlled. By this oral suc- 

 tion method 1 and then 2 blastomeres of the 4-cell stages should be removed. 



Fig. 1. Embryo after spinal cord transection anterior and posterior 

 to the fin at stage 23; conduction restored across anterior 

 lesion. Note localized kyphosis of tail. 



Fig. 2. Embryo resulting after cord transection in trunk region at 

 stage 23. This embryo showed no functional restitution. 



Fig. 3. Cord transection between somites 6 and 7; operation at 

 stage 26. 



Fig. 4. The medulla was separated from spinal cord by transection 

 at stage 26. This embryo showed functional and anatomical 

 regeneration. Note both lordotic and kyphotic curvatures. 



(From Nicholas G Oppenheimer 1942: 

 Jour. Exp. Zool. 90:127) 



B. Removal of Parts of the Germ Ring: Stages #10 to #15. 



The germ ring is so adherent to the underlying yolk that the suction procedure must 

 be used cautiously or the yolk will exude whereupon death follows. 



1. Use the window or decapsulation method, and suck out the ectoderm (only) of the 

 germ ring up to not more than 20% of the ring. Concentrate on those parts of 

 the germ ring distant from the early shield. 



2. Suck out parts of the early neural keel (stage #15), with and without the adjacent 

 germ ring. (Nicholas and Oppenheimer found that if 25% of the keel is removed, 

 development ceases. ) 



C. Ablation Experiments on Later Stages: (Stages #20 to #23 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. 



3. 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. 



