Cell contact and positional communication in hydra.

Positional communication and the functional coupling of muscular reflexes were examined in grafted hydra. A head and distal gastric region inhibited head regeneration by a host sub-hypostome within 4--5 h of grafting. Functionally coupled pathways which indicated the presence of gap junctions also formed between graft and host during this time. It is suggested that gap junctions provide a channel for positional communication.