Abstract
The aesthete organs in the shell of the polyplacophoranChiton olivaceus (Spengler) were studied by scanning and transmission electron microscopy. Compared to previously described species they reveal marked differences. In the upper third of the aesthete, photoreceptor cells have been found. The granula of the club-shaped cells, which fill most of the aesthete, are formed in the proximal part of young aesthetes. The secretory cells located in this part increase in size and become gradually club-shaped. The central cells, hitherto the only known sensory cells in this organ, are very variable in their appearence. The apical as well as the subsidiary caps have pores which penetrate the whole cap in the former, whereas the subsidiary caps are proximally and distally covered by a continous envelope. In contrast, an exchange of substances with the surrounding environment cannot be excluded in the apical cap: there are some indications of secretory processes occurring through the shell surface.
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