THE ORIGIN OF THE NERVOUS SYSTEM IN PENNARIA TIARELLA, AS REVEALED BY TREATMENT WITH COLCHICINE

¹ Wake Forest University, Winston-Salem, NC 27109

Treatment of 8-h embryos of the marine hydrozoan Pennaria tiarella with colchicine for 2 h eliminates interstitial cells, nematoblasts, and ganglionic cells. Comparisons of interstitial-cell-less and control planulae of Pennaria by TEM and light microscopy suggest a dual origin of the nervous system in Pennaria. Ganglionic cells are shown to be derived exclusively from endodermally-derived interstitial cells, whereas neurosensory cells are derived from cells of the ectodermal epithelium, probably from the epitheliomuscle cells. This investigation supports the idea that ganglionic cells and neurosensory cells can differentiate not only from different stem cells but also from different germ layers.