EXPLANATION OF PLATES VI AND yil—Continned. 



Fig. 9. — Section through the twenty-fourth segment of a chick with 

 twenty-nine protovertebrse, showing Wolffian blastema and thin peri- 

 toneal epithelium. Hart, cam., ob. 3. 



Fig. 10. — Section through the twenty-ninth segment of a chick with 

 thirty-four protovertebrse, showing the commencing development of a 

 primary Wolffian tubule from Wolffian blastema. Hart, cam., ob. 4. 



Fig. 11. — Section through a chick, end of third day or beginning of 

 fourth, showing earliest appearance of a secondary tubule. Hart, 

 cam., ob. 3, 



Fig. 12. — Section through the thirty-second protovertebra of a 

 chick with thirty-four protovertebrse, showing the kidney blastema. 



Figs. 13 — 17. — A series of sections from the hind end of a chick of 

 fourth day, illustrating the continuity of the Wolffian body with the 

 cells forming the kidney blastema. Hart, cam,, ob, 3, 



Fig. 13. — Last section, in which a tertiary tubule was seen. 



Fig. 14. — Last section, in which a secondary tubule was seen. The 

 tubules in figs. 13 and 14 are contiguous. 



Fig. 15. —Next section but one behind fig. 14. 



Fig. 16. — Next section but one to fig, 15, 



Fig, 17 a, — Section some distance behind that drawn in fig. 16. 



Figs, 15, 16, and 17 show kidney blastema. 



Fig. 17 shows opening of Wolffian duct into horn of cloaca. 



Figs. 18 — 20. — Sections through a slightly older embryo than that 

 from which above series was taken. Hart, cam., ob, 3, Showing (fia. 

 20), ureter opening into Wolffian duct, with shifted kidney blastema 

 lying just internal to it. 



Fig. 19. — Showing developing ureter and kidney blastema. 



Fig. 20.— Section just anterior to ureter through the anterior end of 

 the kidney blastema. 



Fig. 21. — A longitudinal vertical section through the hind end of a 

 four-day chick, showing continuity of kidney blastema with hindermost 

 part of Wolffian blastema, in which the development of W^olffian tubule 

 is taking place. No line of demarcation can be drawn between the two. 



Fig. 22. — Section through a chick of seventh day or late in sixth, 

 showing the portion of the ureter {ii.) and its dorsal dilatation {v. t.) 

 with regard to the Wolffian body {w.). 



Figs. 23 and 24 are from sections of the chick from which fig. 22 was 

 taken. 



Fig, 23, — Section next but one to fig. 22. It shows the kidney tubule 

 dorsal to the ureter, surrounded by the blastema. 



Fig. 24. — Section next to fig. 23. It shows the dilated termination of 

 the kidney tubule, and the continuity of its lining cells with those of the 

 kidney blastema. 



Fig. 25. — From a section through the kidney of an eight-day chick, 

 showing the termination of a kidney tubule. It presents the same 

 feature as fig. 24. 



