On the occurrence and significance of annulate lamellae in gastrodermal cells of regenerating planarians.

Cytoplasmic annulate lamellae have been observed to occur only in a subset of the gastrodermal cell population of regenerating planarians. They have not been found in the gastrodermal cells of intact, non-injured worms, nor in any other somatic cell type. These observations plus the presence of numerous chromatoid bodies in the same cells are consistent with the hypothesis that these cells are altering their state of differentiation and are preparing for division. It is further suggested that these cells are the precursors to the definitive somatic stem cells, the beta cells.