182 W. F. R. WELDON. 



Granules attached to epithelium of central duct. /. Openiug of head kidney 

 tubules to pericardium. Ly. Lymphatic tissue at posterior end of central 

 duct. pc. Pericardial epithelium. S. D. Segmental duct. s. d. Atropliied 

 portion of segmental duct. v. c. Great vein. x. Strands of blood-vessels 

 passing from glomerulus to lymphatic tissue of head kidney. 



Fig. 1. — View of head kidney of Bdellostoma, from within the pericardium. 

 The segmental duct is seen through the wall of the pericardium. X 4 diam. 



Fig. 2. — Diagrammatic longitudinal section through head kidney of Bdello- 

 stoma. 



Fig. 3. — Transverse section through the middle of the head kidney. The 

 tubules and the central duct are drawn, but the capillaries surrounding the 

 tubules are omitted. Zeiss, obj. a, oc. 2. 



Fig. 4. — Epithelium of central duct, showing granules thrown into its 

 lumen. Zeiss, Obj. r, oc. 2. 



Fig. 5. — Clot from central duct. Obj. f, oc. 2. 



Fig. 6. — Transverse section through the lymphatic tissue at the posterior 

 end of the central duct, showing strands of blood-vessels passing into it from 

 the adjacent glomerulus. Obj. d, oc. 2. 



Fig. 7. — Portion of periphery of a section similar to that shown in Fig. 3, 

 showing the cliaracters of the head kidney tubules and the surrounding blood- 

 vessels. Obj. D, oc. 2. 



Fiss. 3 to 7 drawn with the camera lucida. 



