A STUDY ON THE MODES OF SECRETION BY THE PALLIALEPIDERMICCELLS IN THREE SPECLES OF FRESHWATER PEARLY MUSSELS

The mode of secretion by the pallial epidermic cells were studied in three species of pearly freshwater mussels, by using light microscope,phase contrast microscope,and trans-mission and scanning electron microscopes.The modes of secretion include:partial secretionof vesicle-type and long-foot type;apocrine and rnacroapocrine secretion of split-type andfluid-type;and holocrine secretion in which the secretarv s ubstances are exuded with thewhole cell,or the exocuticle is detached from the formed stratified epithelium. The major secretion modes are vesicle-type and split-type for the endocuticle,and fluid-type andholocrine secretionbrthe exocuticle.The secretion bv the endocuticle is sustained and con-tinuous,and the neighboring cells may show different phases of secretion at the same time. Inthe exocuticle, the secretion appears to be rhythmic and regional;there may be strong secretion activities in one cell region but no secretion activities in another region. The apparentdifferenees in the mode of secretion and property of secreted substances between endocuticleand exocuticle cells mav reflect their di fferences in functions.