| Once a hydranth has begun to develop, it inhibits the production of others proximal to it by the diffusion of an inhibitory substance downward along the stem. |
| In both cases the hydranth is extremely reduced and has no tentacles, and the polyp forms a colony by budding from the base. |
| If a hydra is cut in half, the head end reconstitutes a new foot, while the basal portion regenerates a new hydranth with mouth and tentacles. |
| The polarity in this system is apparently determined by an activity gradient in such a way that a hydranth regenerates wherever the metabolic rate is highest. |
| As a general rule polyp-buds are produced from the hydrorhiza and hydrocaulus, while medusa-buds are formed on the hydranth. |
| Speaking generally, three principal types of hydranth can be distinguished, each with subordinate varieties of form. |
