Tentacle regeneration in Hydra: a quantitative methodological approach.

A quantitative method is proposed for the evaluation of distal regeneration in Hydra attenuata; it is based on estimates of tentacle elongation during 10 days of regeneration, determination of a Tentacle Regeneration Index, and a statistical analysis of profiles obtained from various samples in different experiments. The results show that: polyps under normal conditions have similar regeneration patterns, regardless of individual variability; and ATxII, a neurotoxin of cnidarian origin, produces a statistically significant increase in the Tentacle Regeneration Index. The results are discussed in relation to pattern formation and growth in Hydra.