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1 Department of Biology, University of Victoria, Victoria, B. C., Canada V8W 2Y2, and Bamfield Marine Station, Bamfield. B. C., Canada V0R IB0
Glyoxilic acid induced fluorescence histochemistry and ultrastructural observations indicate that the larval nervous system includes an apical region of neuropile on the oral hood between the anterolateral arms and a ganglion comprised of nerve cell bodies and neuropile on the lower lip of the larval mouth. Electrical stimulation induced metamorphosis more frequently and with a lower mean threshold when a suction electrode was attached to either of these two nerve centers. When the entire oral hood, including oral ganglion and apical neuropile was excised, it and the posterior regions of the larva metamorphose spontaneously. Neither the excised pre-oral hood nor the remaining portions containing the oral ganglion and the adult rudiment metamorphose until exposed to the chemical cue that naturally induces metamorphosis. Excised larval arms do not respond to the natural cue. 10-5 M dopamine induced metamorphosis in a small proportion of larvae, and l0-5 M L-dopa and dopamine induced metamorphic responses in excised larval arms. It is proposed that the apical neuropile and oral ganglion are nerve centers that mediate between the perception of the natural cue and control the initiation of metamorphosis.
Submitted on September 3, 1982
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