Outgrowth of the stolon in the hydroid Cordylophora has been studied at the cellular level. Staining experiments and histological examination indicate that the generative region of the stolon is at its base where interstitial cells are prominent. Cells in the ectoderm at the stolon tip appear to be actively synthesizing new perisarc as the tip advances over the substrate, rather than involved in proliferation. The fine structure of cellular relationships in these regions has been considered and an attempt has been made to correlate the structure and distribution of intercellular attachments with these various functional zones along the outgrowing stolon. Intercellular attachments are similar to those previously described in Hydra, but favorable cases provide a more complete description. The series of intercellular septa each consist of two electron-opaque bodies lying close together midway between the two plasma membranes and separated from the membranes by a region of lesser density. The plasma membranes contain electron-opaque and transparent regions which alternate with the septa. These regions extend over about 70 A. The position of intercellular connections relative to the outer surface of the cenosarc varies in different parts of the stolon.

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