The study of normal and regenerating tetrathyridia shows that 2 tissues of this larva are capable to proliferate by mitosis: a) the apical massif (described by Hess 1980), and b) the pool of germinative cells. The latter occur as dividing forms (light germinative cells) and as migrating forms (dark germinative cells). Dark germinative cells develop into parenchymal muscle cells. The suckers of the tetrathyridia are composed of five different muscle systems, an interstitial syncytium,

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... oring sucker cells, and neurons with different functions. During morphogenesis, the sucker blastema is isolated by fibroblasts from the surrounding tissues. The origin of the blastema cells is discussed.