U08 



EXPERIMENTAL FISH EMBRYOLOGY 



INDUCTION OF SECONDARY EMBRYO BY GRAFTING OF DORSAL LIP 



The fish egg can be uaed as a host for successful transplantations without the neces- 

 sity of a Briicke or bridge to hold the graft In place. Healing and development are so 

 rapid that the whole experiment can he concluded within several days. 



Procedure : 



1. Pass the egg and its chorion through 7 to 10 changes of sterile medium. This 

 should be hypertonic, such as double or triple Standard (Holtfreter' s) Solution. 



2. Decapsulate the egg, using the technique of Nicholas (1927) described above. The 

 steel needles or watchmaker's forceps imist be sterile. Use stage #13 when the 

 germ ring has passed over about 5/*+ of the yolk. Similarly prepare the donor, 



of the same age and stage. 



5. Dissect out of the donor the region comparable to the amphibian dorsal lips, 



i.e., the margin of the germ ring from which arises the embryonic shield. Clear 

 it of all adherent yolk. Use sharp and sterile steel needles. It will help to 

 follow the graft If the entire donor is previously stained in l/lO,000 Nile Blue 

 Sulphate . 



h. Prepare the host for the graft, using two different sites in as many hosts. 

 Operate in double Standard ( BDltfreter's) Solution, or stronger. 



a. Loosen the embryonic shield on one side, using sharp, steel needles. The 

 cells will tend to grow together rapidly, and will hold any graft In place. 

 Insert the excised dorsal lip material, pushing it beneath the margin of 

 the embryonic shield. 



b. Loosen some superficial cells of the extra-embryonic blastoderm at some 

 distance from the embryonic shield, and quickly insert the excised dorsal 

 lip material. 



5. After the wound has healed and the graft seems to be held intact, transfer the 

 embryo (by wide-mouthed pipette) to a covered #2 Stender containing sterile, 

 normal (isotonic) medium for that egg. Culture it for a few hours to as many as 

 7 days, depending upon the success of the take and health of the embryo. 



Localization in the nerve keel 

 of the late gastrula. Cells 

 removed from the region A dif- 

 ferentiate when grafted on ex- 

 tra-embryonic membrane to form 

 optic lobe, cells from the re- 

 gion C to form spinal cord. A 

 defect in the region U resulted 

 In a deficiency in the region of 

 Mauthner's cell. 



An embryo In which 180 germ ring 

 from an early gastrula has formed 

 caudal fin dorsal to the brain of 

 the host. Fixed 8 days after 

 operation. 



(From Oppenheimer 1958: 

 Jour. Exp. Zool. 79:185) 



(From Oppenheimer 1956: 

 Jour. Exp. Zool. 75:'*05) 



