The origin of mucous cells inHydra viridis : II. Mid-gastric regeneration and budding

The origin of hypostomal mucous cells during regeneration and budding has been studied inHydra viridis. NormalHydrae were transected at two levels along their body column - sub-hypostomal and mid-gastric - and the cells which participated in hypostome regeneration were identified histologically and with the electron microscope. An earlier paper in this series (Rose and Burnett, 1968b) showed that zymogen cells transformed to mucous cells in sub-hypostomal regenerates. The work reported in the present paper demonstrates that gastrodermal basophilic cells are the primary source of new mucous cells in animals cut in the mid-gastric region. Evidence is presented to support the thesis that these basophilic cells are derived from epidermal interstitial cells. This choice between zymogen cell versus basophilic cell reflects the distribution of these cells along the parent body column at the sites of the transections.Bud morphogenesis inHydra viridis was also studied because budding provides conditions similar to those of regeneration, and yet, no injury is inflicted on the animal to be studied-that is, a new hypostome must be formed at the distal end of the bud and it must be populated with new mucous cells. The origin of these cells is not from pre-existing mucous cells. The results supported the conclusion that interstitial cells migrate from the epidermis into the gastrodermis of the developing hypostome and differentiate into mucous secretory cells.