The Location of the Chick Embryo. 383 



EXPLANATION OF PLATES. 



Plate I. 



Fig. I. Blastoderm 20 hrs. old. ;f, point of insertion of hot needle before incubation. 



Fig. 2. Ventral view of embryo 48 hrs. old. Injury made in center of unincubated blastoderm 

 lies back of heart. Brain undeveloped. 



Fig. 3. Surface view of forty-hour embryo in which the material along the radius x—y had been killed. 

 Heart, brain and notochord are present. 



Fig. 4. Embryo 30 hrs. after operation described for Fig. 3. Heart and posterior body region 

 present. 



Fig. 5. Primitive streak 18 hrs. old. The three black areas indicate the positions of the injuries 

 made upon the unincubated blastoderm. 



Fig. 6. Surface view of embryo 36 hrs. old. The black areas indicate the wounds x and made 

 in the blastoderm before incubation. 



Fig. 7. Embryo 40 hrs. old. The openings x and indicate the wounds made in the blastoderm. 



Plate II. 



Fig. 8. Embryo 36 hrs. old. The position of the wounds is indicated by the black areas x and y. 



Fig. 9. Embryo 40 hours after injuries were made in the anterior and posterior end of the 18 

 hr. primitive streak. 



Fig. 10. Embryo 12 hours older than that in Fig. 9 after the same operation. 



Fig. II. Forty-hour embryo in which an injury had been made in the posterior end of the primitive 

 streak of 18 hrs. The black region (y) indicates the wound. 



Fig. 12. Embryo incubated 36 hrs. after four-fifths of the material of the primitive streak was 

 destroyed, leaving only the anterior end. 



Fig. 13. Fifty-hour embryo in which the posterior third of the primitive streak (w) was 

 destroyed. The brain which was normal is not shown. 



Fig. 14. Surface view of embryo 30 hours after the middle part of the primitive streak was 

 destroyed. The normal brain is not shown. 



Fig. 15. Embryo of same age as preceding one. The anterior third of the primitive streak 

 was destroyed. Heart and brain which are not given are normal, w in these figures indicates region 

 of injury. 



