{70} Professor Hering is not clear here. Vibrations (if I understand his theory rightly) should not be set up by faint _stimuli_ from within. Whence and what are these _stimuli_? The vibrations within are already existing, and it is they which are the _stimuli_ to action. On having been once set up, they either continue in sufficient force to maintain action, or they die down, and become too weak to cause further action, and perhaps even to be perceived within the mind, until they receive an accession of vibration from without. The only “stimulus from within” that should be able to generate action is that which may follow when a vibration already established in the body runs into another similar vibration already so established. On this consciousness, and even action, might be supposed to follow without the presence of an external stimulus. {71} This expression seems hardly applicable to the overtaking of an internal by an external vibration, but it is not inconsistent with it. Here, however, as frequently elsewhere, I doubt how far Professor Hering has fully realised his conception, beyond being, like myself, convinced that the phenomena of memory and of heredity have a common source. {72} See quotation from Bonnet, p. 54 of this volume. By “preserving the memory of habitual actions” Professor Hering probably means, retains for a long while and repeats motion of a certain character when such motion has been once communicated to it. {74a} It should not be “if the central nerve system were not able to reproduce whole series of vibrations,” but “if whole series of vibrations do not persist though unperceived,” if Professor Hering intends what I suppose him to intend. {74b} Memory was in full operation for so long a time before anything like what we call a nervous system can be detected, that Professor Hering must not be supposed to be intending to confine memory to a motor nerve system. His words do not even imply that he does, but it is as well to be on one’s guard. {77} It is from such passages as this, and those that follow on the next few pages, that I collect the impression of Professor Hering’s meaning which I have endeavoured to convey in the preceding chapter. {78} That is to say, “an infinitely small change in the kind of vibration communicated from the parent to the germ.” {79} It may be asked what is meant by responding. I may repeat that I understand Professor Hering to mean that there exists in the offspring certain vibrations, which are many of them too faint to upset equilibrium and thus generate action, until they receive an accession of force from without by the running into them of vibrations of similar characteristics to their own, which last vibrations have been set up by exterior objects. On this they become strong enough to generate that corporeal earthquake which we call action.