Effects of light— and dark-adaptation on the photic microvilli and photic vesicles of the pulmonate snail Helix aspersa

Intramembranous particles of photic microvilli and microvesicles in light- and dark-adapted garden snails ( Helix aspersa) were studied by electron microscopy of replicas of freeze-fracture faces of villar membranes. More particles adhered to the P (cytoplasmic) faces than to the E (external) faces (particle coefficient between 5 and 80). Particles of 70Ådia were more abundant in photosensitive membranes of dark-adapted snails than in those illuminated with a bright light, the difference being statistically significant. It is concluded that the particles are the photopigment.