G. C. Davenport. — Primitive Streak. 



PLATE V. 



Fig. 20. The sixty-fourth section behind the dorsal notochordal opening of a. 

 See Diagram I., page 6. X 240. 



Fig. 21. The one hundred and twelfth section behind the dorsal notochordal 

 opening of a. X 240. 



Fig. 22. The region marked sui. pr. p. in Fig. 17, more highly magnified. 

 X 420. 



Fig. 23. The region marked sul. pr. p. in Fig. 18, under higher magnification. 

 X 420. 



Fig. 24. Section cut in the direction of the line 24-24, Fig. 5. The ectoderm 

 of a is split at the axis of a. The asterisk marks the point of 

 separation between the entoderm of a, and that of ^. X 73- 



Fig. 25. Section along the line 25-25, Fig. 5. The ectoderm of a is split at 

 the axis of a. One half of the entoderm of a has disappeared to- 

 gether with the anterior floor of /3. X 73- 



Note. — By an oversight o' and B!' have been interchanged in position 

 in this Figure. 



Fig. 26. Section, the position of which is shown by the line 26-26, Fig. 5. 

 The ectoderm of a is split at the axis of a. Part of the entoderm 

 of a, and the anterior part of the floor of the notochordal canal of ft 

 have broken through into the yolk. X 73- 



