Abstract 1. 1. The contractile tissues of Cliona celata were stimulated in various ways. 2. 2. Electrical stimuli were without effect. 3. 3. Pharmacological reagents were believed to have a toxic effect on the choanocytes of Cliona celata. No direct action on the contractile cells was observed. Change in pH had a similarly toxic effect. 4. 4. The response to mechanical stimulation showed a graded response to increase in stimulus strength and a short latent period, but there was no evidence of temporal summation or facilitation. Interpapillar conduction did not occur; intrapapillar conduction was most likely due to stretch.