EXPLANATION OF PLATES VI AND VII, 



Illustrating Mr. SedgwicVs Memoir on '^ Development of 

 the Kidney in its Relation to the Wolffian Body in the 

 Chick." 



Complete List of Reference Letters. 



Ao. Aorta. Al. Alimentary canal, cl. Cloaca, c. v. Cardinal vein. 

 ep. Epiblast. k?/. Hypoblast, i. c. m. Intermediate cell mass. i. c. m.' 

 Cell mass, which later becomes the intermediate cell mass. m. e. 

 Mesentery. M. d. Miillerian duct. k. b. Kidney blastema. k. t. 

 Kidney tubule, n. c. Notochord, p. Protovertebra. p' . Cell mass, 

 which later becomes a protovertebra. p. v. Body-cavity, p. e. Peri- 

 toneal epithelium. t. Testis. u. Ureter. ve. Vertebral body. w. 

 Wolffian body. w. b. Wolffian blastema, w. d. Wolffian duct. w. t} 

 Primary Wolffian tubule, w. t? Secondary ditto, w. t? Tertiary ditto. 



Fig. 1. — Section between the fifteenth and sixteenth protovertebrae 

 of a chick with twenty-three protovertebrae, showing the rudimentary 

 continuation of the body-cavity into the intermediate cell mass and the 

 connection which the latter has obtained with the Wolffian duct. The 

 intermediate cell mass in anterior and posterior neighbouring sections 

 has separated from the peritoneal epithelium. 



Figs. 2, 3, 4, and 5. — Sections taken from a duck embryo with about 

 thirty -two protovertebrae, illustrating the development of the Wolffian 

 tubules. .Hart, cam., ob. 4. 



Fig. 2. — Section through the thirtieth segment, intermediate cell mass 

 continuous with peritoneal epithelium, and containing a rudimentary 

 prolongation of the body-cavity. Lumen of Wolffian duct doubtful. 



Fig. 3. — Section through the twenty-ninth segment, intermediate 

 cell mass separate from peritoneal epithelium. 



Fig. 4. — Section through the twenty-sixth protovertebra, showing 

 features similar to above. 



Fig. 5. — Section through the twenty-second protovertebra ; com- 

 mencing differentiation of Wolffian tubule. 



Figs, 6 — 10, — Sections illustrating the more modified development of 

 the Wolffian blastema, as seen in the chick behind the twentieth segment. 



Fig. 6. — Section through a chick with twenty-six protovertebrae 

 behind the last- formed segment, showing the thick peritoneal epi- 

 thelium, the Wolffian blastema in connection with the mass of cells 

 which will become a protovertebra. Hart, cam,, ob. 4. 



Fig. 7, — Section through the twenty-ninth protovertebra of a chick 

 with twenty-nine protovertebrae, showing the thick peritoneal epi- 

 thelium and the Wolffian blastema in connection with the protovertebrae. 

 Hart, cam., ob. 4. 



Fig, 8, — Section through the twenty-fourth segment of a chick with 

 twenty-six protovertebrae, showing the Wolffian blastema separate from 

 protovertebrae and thick peritoneal epithelium. Hart. cam., ob. 3, 



