G. C. Davenport. — Primitive Streak. 



PLATE XI. 



All figures magnified 73 diameters, except Figure 58, which is magnified 420 



diameters. 



Fig. 54. An oblique section through the notochordal opening of the embryo 



seen in surface view in Fig. 9, Plate II., cut along the line 54. 



This section passes through a lobe of the opening on the left, and 



cuts through the edge of a lobe on the right side. 

 Fig- 55- The third section behind the dorsal notochordal opening. The so 



called plug region is grooved. 



Note. — By a mistake the primitive groove is marked as neurenteric 



canal, can. u'ent. It should have been sul. pr., as in Figure 56. 

 Fig. 56. Sixth section behind the dorsal notochordal opening. The groove 



still persists. 

 Fig. 57. A section near the anterior margin of the shield. A blind canal {can. 



Ht'cd.) exists within the entoderm of this region. 

 Note. — The letters sul. pr. should have been omitted. 

 Fig. 58. Represents under a high magnification the so called plug region seen 

 in Figure 55. 



