DESCRIPTION OF PLATE III, 



Illustrating Mr. Adam Sedgwick's Paper *^ On the Early 

 Development of the Anterior Part of the Wolffian 

 Duct and Body in the Chick, together with some Re- 

 marks on the Excretory System of the Vertebrata.^' 



List of Reference Letters. 



al., alimentary canal j ao., aorta ; c. v., cardinal vein ; e. gl., external 

 glomerulus; ep., epiblast; hy., hypoblast; i. c. m., intermediate cell mass; 

 i. gl., internal glomerulus ; k. b., blastema of Wolffian tubules ; me., mesen- 

 tery; »i. I?., muscle plate; ;?(?., notochord; ;?. c, body cavity ; ^./., peri- 

 toneal funnel; ^y., proto-vertebra ; j9p.', cell-mass, which later becomes a 

 protovertebra ; W. d., Wolffian duct ; W. t., Wolffian tubule. 



Fig. 1. — Section through 10th segment of a chick with ten segments, 

 showing origin of Wolffian duct. 



Fig. 2. — Section through 10th segment of a chick with twelve segments. 

 Shows second stage in development of Wolffian duct. 



Figs. 3 and 4. — Successive sections through the 10th segment of a chick 

 with thirteen segments. Shows further development of Wolffian 

 duct. 



Fig. 5. — Section through 10th segment of a chick with fourteen segments, 

 showing further development of Wolffian duct and anterior Wolffian 

 tubules. 



The above series are all taken through the points where rudimen- 

 tary segmental tubes connect the Wolffian duct and peritoneal epi- 

 thelium, except Fig. 4, which is through a point between two tubules. 

 The object of the series is to trace the continuity in the development 

 of the Wolffian duct and anterior tubules, which exists between the 7th 

 and 11th segments inclusive. 



j'lQ, 6. — Section through a chick with twelve segments just behind the 

 12th segment. Shows independence of Wolffian duct from peritoneal 

 epithelium and intermediate cell mass. 



j'lQ, 7. — Section through the 13th segment of a chick with thirteen seg- 

 ments. Shows how almost at once the Wolffian duct becomes con- 

 nected with the intermediate cell mass. The continuity between the 

 two structures is not well represented in this figure. 



Fig. 8. — Section through 16th segment of a chick with twenty-one seg- 

 ments. Shows separation of Wolffian duct and intermediate cell 

 mass, which persists for some time in this region. 



Figs. 9 and 10. — Successive sections through the 15th segment of a chick 

 with about twenty-two protovertebrse, 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. 



