226 ^- ^- PRICE, Develoi.nierit of the Excretory Organs of Bdellostoma. 



Explanation of Plates. 



ao aorta. pr. t pronephric tubule. 

 b. c body-cavity. s. d segmental duct. 



B. c Bowman's capsule. s. t segmental tubule. 



ch chorda. sp. C spinal cord. 



coe.p coelomic pocket. sp.g spinal ganglion. 

 gl glomerulus. v.r ventral root. 



my myotome. 



Figs. 1 — 10 are from stage A, and Figs. 1 — 8 are from the same 

 embryo. 



Plate 16. 



Fig. 1. Transverse section through the body of an embryo, showing 

 the relation of the excretory organs to other parts of the body. 



Fig. 2. The most anterior tubule anläge. 



Fig. 3. Anlage of the segmental duct between the second and 

 third tubules. 



Fig. 4. Anlage of the segmental duct between the third and fourth 

 tubules. 



Fig. 5. The fourth segmental tubule. 



Fig. 6. Diagrammatic longitudinal section of the anterior end of 

 the excretory system. 



Figs. 7 a — 7j. Complete series through the eleventh and twelfth 

 tubules, and the connecting portion of the segmental duct, showing the 

 manner of formation of the duct. 



Figs. 8 a — 8g. Series through the duct and tubules in the thirty- 

 fifth segment, showing a coelomic pocket, and the way in which the 

 lumen of the tubule grows back into the duct. 



Figs. 9 a — 9f. Series through duct and tubule in the twenty-first 

 segment of a younger embryo, showing the manner of formation of a 

 coelomic pocket. 



Plate 17. 



Fig. 10. Section through a tubule and coelomic pocket from about 

 the middle of the mesonephric region. 



Fig. 11. Longitudinal section of duct and tubules through six 

 segments in stage B, showing the process of canalization of the duct. 

 Reconstructed on millimeter paper. 



Fig 12. Section through a tubule and coelomic pocket in stage 

 B, showing the beginning of the formation of a glomerulus. 



Fig. 13. Section of duct and Malpighian corpuscle in stage C. 

 Fig. 14. Longitudinal section through a tubule and Malpighian 

 corpuscle in stage C. 



Figs. 15 and 16. Two sections through the pronephros in stage C. 



