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Ultrastructural and histochemical studies of the differentiating plerocercoid cuticle of Schistocephalus solidus Morris, Gerald Patrick

Abstract

To date, most studies of the cestode cuticle have been carried out on adult worms and in no instance has an attempt been made to correlate ultrastructural and histochemical observations. The present study was designed to obtain information on both the histochemical composition and the ultrastructure of the plerocercoid cuticle of the pseudophyllidean cestode Schistocephalus solidus (Müller, 1776) and to study any changes which might occur during plerocercoid differentiation. Initially, this work has demonstrated that the plerocercoid tegument of S. solidus is of the same fundamental type as that of previously described cestodes. An outer anucleate but cellular region (the cuticle) is connected by cytoplasmic tubes to nucleated tegumental cells lying in the parenchyma. It has been shown that the pore canals of S. solidus are different from any described for other cestodes and it is suggested on morphological grounds that they may function in a secretory capacity. In addition, the pore canals provide a direct connection between certain parenchymal cells and the external medium. Papilla-like cuticular processes on the cuticular surface have been described and both adhesive and absorptive functions are suggested for these structures. It has been shown that the cuticular processes are not present in the smallest forms studied but rather appear at about the same time as the worm becomes infective. Changes in the histochemical and ultrastructural composition of the cuticular matrix have been described. It is probable that increased plerocercoid growth is accompanied by a change in cuticular composition from a more proteinaceous state to one which is largely carbohydrate. A surface sulphomucin-basic protein complex has been described and partially characterized. Possible functions have been suggested for this layer. RNA as well as acid and alkaline phosphatases were found in the cuticle and the possible significance of these substances in cuticular synthetic activities is considered. It is suggested that plerocercoid cuticular differentiation may consist of two phases: (1) an initial phase in which various mechanisms are elaborated to allow survival in the vertebrate intestine, and (2) a second phase in which the plerocercoid is modified to permit prolonged growth in the stickleback coelom.

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