G. C. Pavenport. — Primitive Streak. 



PLATE X. 



Figures 49-51 are magnified 73 diameters; Figures 52 and 53, 240 diameters. 



Fig. 49. The tenth section behind the dorsal notochordal opening of an em- 

 bryo which closely resembles in surface view Fig. 7, Plate II. 



Fig. 50. Third section behind the dorsal notochordal canal of the same em- 

 bryo. The so called plug region is grooved. 



Fig. 51. Representation of the third section behind the dorsal notochordal 

 opening of the embryo seen in surface view in Fig. 13, Plate III. 



Fig. 52. Third section anterior to the dorsal notochordal opening of the em- 

 bryo seen in surface view in Fig. 11, Plate III. The halves of 

 the anterior lip are still fusing. 



Fig- S3- Third section behind the dorsal notochordal opening, from the same 

 embryo as the preceding figure. 



