Behavior in Hydra: Contraction Responses of Hydra pirardi to Mechanical and Light Stimuli

Hydra pirardi c ontracts in response to light and mechanical agitation. The animals show a reduction in the number of contractions in response to mechanical agitation on repeated testing but continue to contract in response to a light stimulus. Excision of all the tentacles of the animal completely inhibits contraction in response to mechanical agitation but does not affect contraction in response to light. The results of these experiments suggest that H. pirardi has different receptors for light and for mechanical agitation and that the control mechanisms for the contraction responses to these two stimuli are independent.