DESCRIPTION OF PLATE ILliNl— continued. 



Figs. 9 and 10. — Successive sections throuf^li the 15th segment of a chick 

 with about twenty-two protovertebrae, showing the connection between 

 the Wolffian duct and intermediate cell mass. In Fig. 9 the inter- 

 mediate cell mass is continuous with the peritoneal epithelium ; in 

 Fig. 10 it is separate. 



Fig. 12. — ^Section througli a chick late in the third day behind the 16l,h 

 segment, showing the independence of the developing Wolffian tubule 

 and the Wolffian duct in this region. 



Figs. 13, 14, and 15.— A series of successive sections through the 13th 

 segment of a chick with thirty-one or thirty-two segments. Fig. 13 

 being anterior. Show a further stage in the development of a Wolf- 

 fian tubule in this region. In Figs. 13 and 14 the tubule is connected 

 to the peritoneal epithelium, and a lumen has appeared in it, which 

 is continued behind into the part of the tubule separated from the 

 peritoneal epithelium, seen in Fig. 15. 



Figs. 16, 17, and 18. — Sections through the 13th or 14th segment of a chick 

 with thirty-four or more segments. Show the further devehipment of a 

 Wolffian tubule in this region, and the first appearance of the external 

 and internal glomeruli. Figs. 16 and 17 are contiguous sections. 

 Between Figs. 17 and 18 there is a section not figured. The three 

 figures respectively correspond to and are further developments of 

 Figs. 13—15. 



Figs. 19, 20, and 21. — Successive sections through the 13th or 14th seg- 

 ment of a chick with thirty-six or more segments. Show further de- 

 velopment of external glomerulus. 



Fig. 22. — Diagrammatic longitudinal, vertical section, showing the rela- 

 tions of the external and internal glomerulus. 



Fig. 23. — Section through the 13th or 14th segment of a chick with i hirty- 

 three segments, showing the opening of the Wolffian duct near the 

 external glomerulus. 



Fig. 24. — Section through the anterior part of the Wolffian body of a 

 4th day chick, showing the glomerulus projecting into the Wolffian 

 duct. 



Fig, 25.— Section through the hinder region of a tadpole of Rana tern- 

 j)orania, showing the first appearance of the cells from wliich the 

 Wolffian tubules will arise. 



