82 



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 

 diam. 



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. Z 



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. 



Fig. 28. Transverse section through two adjacent bran- 

 chial filaments, showing the interfilamentar 

 junction. X about 600 diam. 



