115 



Plate IV. 



Fig. 19. Transverse section of the secreting portion of 

 the byssus gland. The section is cut trans- 

 versely to the long axis of the foot. X 60 

 diani. 



Fig. 20. Longitudinal section through a single alveolus of 

 the byssus gland. X 570 diam. 



Fig. 21. Vertical section through part of the body- wall 

 of the distal limb of the viscero-pedal mass, 

 showing a mucous gland cell opening through 

 the epidermis on to the surface of the foot. 

 Zeiss apo. 1"5 mm., compens. oc. 12. 



Fig. 22. An isolated mucous gland from the distal limb 

 of the viscero-pedal mass. Zeiss apo. 1"5 mm., 

 compens. oc. 12. 



Fig. 23. A radial vertical section of the mantle edge. X 

 30 diam. 



Fig. 24. A section through the internal labial palp, pas- 

 sing parallel to the longest border. X 80 diam. 



Fig. 25. Vertical section through the muscular body- wall 

 of the proximal limb of the viscero-pedal mass. 

 X 120 diam. 



Plate V. 



Fig. 26. Part of a section through a branchia, transverse 

 to the branchial filaments, and including two 

 groups of filaments. X 80 diam. 



Fig. 27. Transverse section of a single branchial filament. 

 Zeiss apo. 1'5 mm., compens. oc. 4. 



JFig. 28. Transverse section through two adjacent bran- 

 chial filaments, showing the interfilamentar 

 junction. X about 600 diam. . 



