ABSTRACT
In the precedingchapter it was pointed out that in a unicellular animal the ability to receive stimulations from the outside world, or sensitivity, and the ability to move in response to stimulations, or contractility, both reside in the single cell which constitutes the animal’s body. One can think of both sensitivity and contractility at this low level of life as phases of a single process of internal excitement. When the outer surface of the body of a unicellular animal comes in contact with an object, the molecules of the protoplasm are set in motion, and there is inner agitation. This agitation results in a redistribution of the molecules, thus producing movements of the body.
