The inhibition of hypostome formation in hydra has been investigated using isolation and transplantation techniques.

The transmission of inhibition does not seem to be polarized; a hypostome situated at the proximal end of the digestive zone can inhibit distal regeneration with no change in regeneration polarity. The time required for the proximal hypostome to establish an effective inhibitory ‘field’ is about 4–7 h. The results confirm that inhibition and polarity are quite separate factors.

The transmission of inhibition by a digestive zone is impaired by treating the region with media containing reduced concentrations of Ca2+ and Mg2+. This treatment has no effect on the inhibitory activity of the hypostome, nor on the resistance of the tissue to inhibition.

The effect of divalent cations on the transmission of inhibition does not seem to be due to an effect on cell adhesion. There is an effect on general cell permeability but this is not temporally correlated with the effect on transmission.

It is suggested that transmission of inhibition is dependent upon contact-mediated intercellular communication, possibly involving functional coupling between cells.

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