Nowadays we attribute the greatest importance to the morphology of the brain, to its histological structure, the marked development of certain regions, the determination not only of centers but of connections and associations between centers. On this last point contemporary anatomists have given themselves up to eager researches, and, although the cerebral architecture is not conceived by all in the same way, it is proper for psychology to note that all with their "centers" or "associational system" try to translate into their own language the complex conditions of mental life. Since we must choose from among these various anatomical views let us accept that of Flechsig, one of the most renowned and one having also the advantage of putting directly the problem of the organic conditions of the imagination. We know that Flechsig relies on the embryological method--that is, on the development--in the order of time, of nerves and centers. For him there exist on the one hand sensitive regions (sensory-motor), occupying about a third of the cortical surface; on the other hand, association-centers, occupying the remaining part. So far as the sensory centers are concerned, development occurs in the following order: Organic sensations (middle of cerebral cortex), smell (base of the brain and part of the frontal lobes), sight (occipital lobe), hearing (first temporal). Whence it results that in a definite part of the brain the body comes to proper consciousness of its impulses, wants, appetites, pains, movements, etc., and that this part develops first--"knowledge of the body precedes that of the outside world." In what concerns the associational centers, Flechsig supposes three regions: The great posterior center (parieto-occipito-temporal); another, much smaller, anterior or frontal; and a middle center, the smallest of all (the Island of Reil). Comparative anatomy proves that the associational centers are more important than those of sensation. Among the lower mammals they develop as we go up the scale: "That which makes the psychic man may be said to be the centers of association that he possesses." In the new-born child the sensitive centers are isolated, and, in the absence of connections between them, the unity of the self cannot be manifested; there is a plurality of consciousness.