EXPERIMENTAL FISH EMBRYOLOGY 



393 



Parts to be cultured at stages #12 or #13: 



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, # 1 5 to #24: 



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 nerve and notochord of stage #20. 



f. Pectoral fin of stage #24. 



Figs. 9 to 15. Sections througli isolated blastoderms which have undergone gastrula- 

 tion and have formed embryonic structures. 



Fig. 9. The ear region of the embryo shown in Fig. 8. The organs are in their 



topographically normal relationships. B, hind -brain; E, ear; P, periblast. 



Figs. 10 and 11. Two sections through an embryo whose structures are in topiograph- 

 ically 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, trans- 

 versely. In Fig. 10, optic vesicles (C), forebrain and optic lobes (B), and 

 periblast are seen, and in Fig. 11 medulla (NV), notochord (N), gut (G) 

 and ears (E). Posteriorly in the head 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 ventral (E) rather than lateral, however, due to twist- 

 ing of the embryonic axis; the notochord is somewhat contorted, and 

 posteriorly grades off into a dense group of cells continuous with the 

 nervous system. (256-celled; 4 days. ) 



Fig. 13. Sagittal section through an embryo in which grain (B), gut (G) and ear 

 (E) are in their normal positions, but the notochord (N) is greatly con- 

 voluted 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 

 gastrulation. A floor plate has been formed only in regions where the 

 notochord (N) and nervous tissue (NV) are in contact. (32-celled; 4 days.) 



(From Oppenheimer 1936: Jour. Exp. Zool. 72:247) 



