Uo6 



EXPERIMENTAL FISH EM3RY0L0GY 



Parts to be cultured at stages #12 or #15= 



a. Portion of the germ ring 180° from the embryonic shield. 



b. Embryonic shield and related germ ring In half embryo. 



c. Dorsal lip material only, i.e., margin of the embryonic shield. 

 Parts to be cultured at later stages, #15 to #2l4-. 



a. Embryonic shield alone at stage #15. 



b. Optic vesicle of stage #17. 



c. Melanophores of extra- embryonic membrane, stage #20. 



d. Heart anlage of stage #20. 



e. Somites and related neiire and notochord of stage #20. 



f . Pectoral fin of stage f2k. 



If the period of isolation can be extended to more than h days it will be neceseaiy 

 to renew the culture medium at that time. Generally the limit of differentiation will be 

 achieved before that time, usually within kQ hours. If the cvilture is made in a hanging 

 drop (see chick exercises) the complete process of development can be observed under the 

 dissecting microscope without disturbing the explant, and if It is bacteria-free, it 

 should survive. 



Figs. 9 to 15. Sections through isolated blastoderms wlilch have undergone gastrulatlon 

 and have formed embryonic structures. 



Fig. 9. The ear region of the embryo shown In Fig. 8. The organs are In their topo- 

 graphically normal relationships. B, hlnd-braln; E, ear; P, periblast. 



Figs. 10 and 11. Two sections through em embryo whose structures are in topographically 

 normal relationships although periblast (P) is found only In the eye region. The 

 embryonic axis was curved, therefore the eye region, shown In Fig. 10, was cut 

 frontally, and the ear region, shown in Fig. 11, transversely. In Fig. 10, optic 

 vesicles (0), forebraln and optic lobes (b) , and periblast are seen, and In Fig. 11 

 medulla (NV) , notochord (N) , gut (G) and ears (E) . Posteriorly in the liead the 

 embryonic axis Is double, and the secondary nervous system Is imperfect. (64- to 

 128-celled; 4 days.) 



Fig. 12. Sagittal section through an embryo in which gut (G) , notochord (N) , medulla (NV) 

 and heart (H) show In general typical relationships to each other. One ear is ven- 

 tral (E) rather than lateral, however, due to twisting of the embryonic axis; t)ie 

 notochord Is somewhat contorted, and posteriorly grades off Into a dense group of 

 cells continuous with the nervous system. (2.")f)-celled; 4 days.) 



Fig. 13. Sagittal section t)irough an embryo In which grain (B) , gut ((!) and ear (R) are 



in their normal positions, but the notochord (N) is greatly convoluted and forms a 

 mass without association with the nervous system. (64-celled; 4 days.) 



Figs. 14 and 15. Two sections through a blastoderm in which irregularities of the nervous 

 system have resulted from the distortion of the substrate after gastrulatlon. A 

 floor plate has been formed only in regions where the notocliord (N) and nervous 

 tissue (NV) are In contact. (32-celled; 4 days.) 



(From Oppenheimer I956: Jour. Exp. Zool. 72:2^7) 



