390 



EXPERIMENTAL FISH EMBRYOLOGY 



Fig. I. Dorsal and lateral views of a Fundulus after hatching revealing the shortening of the head with 



orbital formation following ablation of the eye at stages 21-23. 

 Fig. 2. Stage 27 embryo showing the recovery and healing of an embryo after the removal of the eye 



in Stage 22. Indications of the future mouth and head asymmetry are already evident. 

 Fig. 3. The healing after operation at Stage 22 shows a puckering of the opercular region following 



the removal of fin tissue. The embryo is slightly bent toward the side of operation. 

 Fig. 4. The removal of the fin in Stages 20-22 gives rise always to the type of animal here shown at 



the time of hatching. 

 Fig. 5. The ear was removed in its early vesicle stage, Stage 20. At the time of operation slight 



damage was done to the right half of the brain which is reduced in size. The C curvature is 



characteristic of the posture of the earless forms. 

 Fig. 6. The operation performed at Stage 17 involved a slight injury to the mid-brain and the con- 

 strictions made by the pipette are still evident at Stage 25 anterior and posterior to the original 



site of injury. 

 Fig. 7. The result obtained by on injury to the anterior port of the medulla; the circular region shows 



a deficit extending to the notochord which was slightly enlarged. There is no reconstitution. 



Operation performed at Stage 18. 

 Fig. 8. Development without repair after injury to the left side of the brain. Operation performed at 



Stage 18. 

 Fig. 9. The free portion of the tail bud of a stage 20-embryo was removed. The wound healed and 



was covered with epidermis. The rounded eminence is a notochordal projection covered 



with epithelium. Embryo Stage 25. 



(From Nicholas G Oppenheimer 1942: Jour. Exp. Zool. 90:127) 



Injury or ablations of the embryonic shield and neural keel generally show localized ef- 

 fects, particularly when they occur in the midline of the embryonic axis. After organ 

 differentiation, the damage tolerated must be only a small fraction (less than 10%) of the 

 available tissue. This applies particularly to the formed brain, sense organs, fin, tail, etc. 



In all of this type of work it must be remembered that some of the results may be due to 

 incidental handling of the embryo, as in decapsulating. Also, it is somewhat more dif- 

 ficult to excise a specific region, and only that region, in fish than in the amphibian (or 

 even chick) embryos. Collateral injuries may be the primary cause of failure in recon- 

 stitution. Operational skill with fish material is achieved only with great patience, per- 

 sistence, and repetition. 



