A considerable portion of the second and principal part of this work is occupied with the psychology of attention and of the related subject memory. The latter is defined by M. Hirth as “a sum of states of perception gradually accumulated by the various organs of sense,” and it is thus not a special faculty of the mind. The mental condition which results from the action of memory is what is known as _disposition_. This disposition is transmitted from one generation to another, and becomes innate as the memory of the species. But it is intimately connected with the nervous system, and with the brain regarded as the electric storehouse of memories. It is in accordance with these ideas that the author explains the transmission of hereditary qualities, the problem which is at present engaging so much attention. The innate organisation is a conservation of nervous quality or temperaments associated with the anatomical disposition of the nervous system, and a certain condition of electrical tension among the cerebral molecules. The transmission of ancestral qualities depends, however, on the vigor and good condition of the germ, and as the organisation received from our earliest ancestors is the most persistent, the primitive “disposition” will subsist even without exercise whilst nutrition and circulation assure the continuance of molecular growth. It is with the visual memory that the author is chiefly concerned, and he affirms that the optical phenomena referred to in the Introduction compel us to admit the existence in the brain of a central organ, which he terms the internal eye. In order to determine the position of this organ, which is the real seat of visual perception, to the exclusion of the retina, whose function has been overestimated, M. Hirth considers the anatomical and physiological aspects of the question, and he accepts the conclusion arrived at by H. Munk in his _Functions de l’écorce cerebrale_, that perception is the function of a particular portion of the cerebral cortex. There thus exist two visual centres or “internal eyes,” one in each convexity of the occipital lobes, as shown in Plate V. of the present work. Munk’s researches would seem to prove, moreover, that not only is there a general localisation of visual memories, but that each memory is fixed in a precise and determined place. The centres of memory and the centres of perception, which M. Hirth supposes to be simply a phase of memory, are the same. Moreover attention is connected with perception, but it is an imperfect state of memory. Attention requires the expenditure of force, while perfect memory acts spontaneously; and it is only in this form, “exempt from fatigue, that it becomes the passive servant of our instincts and sensations, of our voluntary acts, of our labor.” Memory when perfect is automatic, and according to the theory of M. Hirth, who does not accept M. Ribot’s monoideistic theory, it is