1. It has been shown that a single large bipolar nerve cell in the subumbrella epithelium of Aurellia is necessary and sufficient to conduct the contraction wave across a narrow bridge from one part of the bell to another.
2. This nerve impulse is accompanied by an electrical impulse of the kind usually recorded from the nerves of higher animals.
3. These nerve cells are concerned only with the excitation leading to a contraction wave. There must be other pathways for other transmitted excitation.