68 LIBBIE H. HYMAN. 



EXPLANATION OF PLATES. 



PLATE I. 



FIGS, i and 2. Two stages in the disintegration of an early blastoderm of 

 Tautogolabrus, showing greater susceptibility of the central cells. 



FIGS. 3 and 4. Two stages in the disintegration of an early blastoderm of 

 Fundulus, showing rupture and disintegration of the central region. 



FIG. 5. Disintegration of an early blastoderm of the cod, showing greater 

 susceptibility of the margin. 



FIGS. 6 and 7. Disintegration of a later blastoderm of the cod, showing 

 greater susceptibility of one region of the circumference and spread of disin- 

 tegration in both directions from this region. 



FIG. 8. A later blastoderm of Tautogolabrus-, posterior half of the blasto- 

 derm most susceptible. 



FIGS. 9 to ii. Disintegration of a late blastoderm of Tautogolabrus. Fig. 

 9, the normal blastoderm; Fig. 10, bulging of the blastoderm up from the yolk 

 and disintegration of the central posterior region; Fig. n, further course of 

 disintegration. 



FIG. 12. First appearance of the germinal shield in the cod. 



FIGS 13 and 14. Disintegration of a stage like Fig. 12. Fig. 13, disinte- 

 gration of the shield; Fig. 14, spread of the disintegration around the germ 

 ring. 



FIG. 15. First stage in the disintegration of a later stage of the embryonic 

 shield of the cod; disintegration beginning at the anterior end of the shield. 



