Asexual reproduction in Microstomum lineare (Turbellaria). I. An autoradiographic and ultrastructural study

The distribution of cells preparing for proliferation during asexual reproduction by paratomy in Microstomum lineare (Turbellaria) was investigated using the technique of exogenous tritiated thymidine (³H]T) labelling and routine electron microscopy. The subsequent fates of labelled cells in developing and mature zooids were followed by fixing tissues at various intervals. The only labelled cells are mesenchymal and gastrodermal neoblasts, occurring along the whole worm without any special growth zones or axial gradient. Organ primordia develop as a result of locally dividing as well as of migrating cells.