EXPLANATION OF PLATES XYII AND Continued. 
Fig. 9. — Section through the twenty-fourth segment of a chick with 
twenty-nine protovertebrae, 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 (fig. 
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 Wolffian 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 {u^ 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. 22, 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. 
