Studies on regeneration blastemas of the planarianDugesia tigrina with special reference to differentiation of the muscle-connective tissue filament system

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Abstract
Head blastemas in regeneratingDugesia tigrina (Planaria) have been studied light microscopically and electron microscopically. Acid phosphatase activity has been followed in early blastemas using a light microscopical cytochemical method. The possibilities of a collagen synthesis inhibiting substance α-α′-dipyridyl in analyzing fibrillogenesis in planarians have been explored. Following a brief discussion of the neoblast concept the general organization and characteristics of the blastema are described. Regeneration of the muscle-connective tissue filament system including the subepidermal membrane is analyzed in detail. It is stressed that the muscle cells, the filamentous sheaths and the subepidermal membrane in planarians should be visualized as a mutually dependent, integrated system. The hypothesis is proposed that neoblasts differentiate into myoblasts which both synthesize myofilaments and collagen. Collagen forms the filaments of the subepidermal membrane-muscle sheath system. No certain interference with collagen synthesis and secretion could be demonstrated in the experiments involving α-α′-dipyridyl. There was no evidence for significant changes in the activity and pattern of acid phosphatase during early stages of regeneration. The problems concerning the existence of neoblasts, their participation in regeneration and their origin (stock cell or result of a dedifferentiation process) are discussed.