42 OSBORN. [Vol. XVIII. 



EXPLANATION OF PLATE L 



All the figures are made from camera lucida drawings, unless otherwise 

 noted. 



Fig. I. View of Anodonta opened so as to display the surface of the 

 kidney, and two specimens of Cotylaspis in situ, nat. size. 



Fig. 2. Young Cotylaspis killed with Hermann's fluid with oral sucker 

 distended, X 44. 



Fig. 2, o. Dorsal view of living Cotylaspis very much contracted from 

 life, without camera. 



Fig. 2, b. View of a living specimen in successive attitudes, X 14. 



Fig. 3. Dorsal view, combined from life and from total prepara- 

 tions, X ZZ- 



Fig. 4. Ventral view, X 30. 



Fig. 5. Side view, idealized, X 45. 



Fig. 6. Sagittal section in plane of cirrus, X 40. 



Fig. 7. Transverse section, anterior region, in line ab of Fig. 6, X yy. 



Fig. 8. Transverse section, posterior region, in line cd of Fig. 6, X yy. 



Fig. 9. Tangential section just below the surface, near the anterior 

 end, X 293. 



Fig. 10. Two muscle fibers from section, iron-hsematoxylin, X 850. 



Fig. II. Myoblast from methylene-blue preparation, without camera. 



Fig. 12. Body-wall and origin of diaphragm at Cr. S. of Fig. 6, X 320. 



Fig. 13. Unicellular gland-cells of parenchyma,from mouth funnel, X 850. 



Fig. 14. Unicellular glands, deeper portion, from vicinity of pharynx, X 567. 



Fig. 15. Mouth and prepharynx from horizontal section, X 200. 



Fig. 16. Pharynx, oesophagus and intestine in section, showing the rela- 

 tion of cuticle and epithelium, X 440. 



Fig. 17. Intestinal epithelium cells in section, iron-hsematoxylin, X 567. 



Fig. 18. Wall of intestine in section passing in the muscle layer, X 270. 



Fig. 19. Sagittal section in the plane of the excretory pore, the right side 

 is anterior, X 425. 



Fig. 20. Horizontal section in plane of excretory bladder and collecting 

 vessel, X 425. 



Fig. 21. Wall of the excretory bladder, showing the degenerating 

 epithelium, iron-hsematoxylin, X 850. 



Fig. 22. Excretory collecting vessel, X 850. 



Fig. 22). Principal vessels of the excretory system, the arrows show the 

 direction of the current, without camera. 



Fig. 24. View from life to show relation of flame cells and capillaries to 

 the larger vessels of the excretory system. 



Fig. 25. View from life of the relation of the collecting and recurrent 

 vessels, and of a capillary crossing them. 



Fig. 26. Flagellum from one of the excretory vessels. 



Fig. 27. Flame cell and capillary, from living compressed specimen. 



