Abstract
Regeneration by anterior and posterior substrates (having a single transection each), indicated presence along anteroposterior axis of three morphogenetic regions. (1) A region of unipotential capacity from 16/17 anteriorly, in which all morphologically determined regenerates were cephalic, with a section from 6/7 anteriorly in which regeneration was obtained only anteriorly. (2) A region of bipotential capacity in which morphologically determined regenerates were cephalic or caudal. Apparent directional limitations of bipotentiality enabled recognition of three sections: 17/18 to 22/23 (→ 27/28?) in which regenerates at anterior transections were all cephalic but at posterior transections were cephalic or caudal or cephalocaudal; a long middle section in which all anterior regenerates were cephalic and all posterior regenerates were caudal; a posterior section in which regenerates at anterior transections were cephalic or caudal or cephalocaudal but at posterior transections were all caudal, tentatively bounded by 176/177 and 200/201. (3) A region of unipotential capacity in which all morphologically determined regenerates were caudal. Experiments were not extended to permit recognition of a terminal section in which regeneration would only take place posteriorly.
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