CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 509 
Fig. 22. Ditto, through the body of the epithelial cells, a. Rod or pro- 
longation of the sensorial cell. b. Membrane of the epithelial cells. 
c. Striae of this membrane, d. Fibroid secretion. 
Figs. 23 — 23. — Pneumodermon. 
Fig. 23. Part of a transverse section of a sucker, showing how the 
longitudinal muscles of the peduncle are inserted on the muscular disc. 
a. Longitudinal muscular fibre of the peduncle, b. Its pointed ex- 
tremity. c. Epithelium of the upper face of the sucker, d. Prismatic 
cells of the muscular disc. 
Fig. 24. Transverse section of a prismatic muscular cell. a. Prism of 
muscular fibres, b. Nucleus. 
Fig. 25. Longitudinal section of a prismatic muscular cell. a. Nucleus. 
