The conclusion is forced upon me that _the hypnoidal state is the primitive rest-state out of which sleep has arisen in the later stages of evolution. We may say that sleep and hypnosis take their origin in the hypnoidal state_.[8] Sleep and hypnosis are highly differentiated states; they have evolved out of the primitive, undifferentiated, hypnoidal state which is essentially a subwaking rest-state characteristic of early and lowly-organized animal life. _The hypnoidal state is the primordial sleep state._ The development of the hypnoidal state into sleep has proven itself useful in the struggle for existence of the higher animals; it has, therefore, become fixed as the rest-state, characteristic of the higher representatives of animal life. Hypnosis and other trance-states, variations of the primitive hypnoidal rest-state, have become eliminated as useless and possibly harmful to the normal life adjustments of the higher animals and can only be induced under artificial conditions in but a fraction of the human race. The hypnoidal state is the normal rest-state of the lower vertebrates and invertebrates. The rest or sleep state of the lower animals is a sort of passive waking state,--a subwaking state which has survived in man as the hypnoidal state. Of course, the state has been largely modified in man by the course of evolution, but it can still be clearly detected, just as the tail of the simian can be discerned in the human coccyx, or as the structure of the prehensile hand of the quadrumana can be still clearly traced in the foot of man. Waking, hypnoidal, and sleep-states may be termed _normal_ states, while _hypnosis_ and various other trance-states may be termed _sub-normal_ states. The relation of the hypnoidal state to waking, sleep, hypnosis, and other subconscious states may be represented by the diagram on following page. The hypnoidal state is normal, it is present in all representatives of animal life. Sleep, hypnosis, and trance-states are variations of the fundamental hypnoidal state. The sleep-state has proven useful and has become normal in the higher animals, while hypnosis like animal “cataplexy” and the various forms of trance-states, likewise variations of the fundamental hypnoidal state, characteristic of man, have not proven of vital value, and have fallen below the normal stream of consciousness with its concomitant adaptive reactions. [Illustration: DIAGRAM II]