Field. — Pronephros in Amphibia. 



PLATE II. 



All the Figures on this plate are magnified 110 diameters. 



Figs 11 and 12. Portions of two frontal sections through the pronephric thicken- 

 ing of one of the older embryos belonging to Stage III. 



Fig. 11 shows the dorsal margin of the thickening. 



Fig. 12 shows a section through the nephrostomal region. 



Figs. 13 and 14. Portions of two frontal sections from one of the younger embryos 

 of Stage II. 



Fig. 13 shows the ventral ends of the anterior protovertebrae. 



Fig. 14 shows a section through the dorsal portion of the pronepliric thickening. 



Figs. 15-17. Portions of three cr«ss sections through one of the younger embryos 

 of Stage III. 



Fig. 15 shows the anterior end of the pronephric thickening. The plane of the 

 section passes a little behind the middle of Somite II. 



Fig. 16 shows the pronephric thickening in the region of Somite V. 



Fig. 17 shows the thickening near its posterior termination. 



