The complexity of the reflex movements which are produced through the lower brain indicates a corresponding complexity in the apparatus concerned. In accordance with this, we find that whilst only one kind of nerves capable of carrying impulses from the surface to the nerve-centres enters the spinal cord, to the lower brain pass not less than five distinct varieties of afferent nerves, which carry impulses of as many different characters to the centres. Contact is necessary to arouse reflex movements through the spinal cord. The effect of a pistol report upon a brainless animal demonstrates, however, that its nerve of hearing is capable of carrying to the middle brain an impulse which stirs that centre to action. The brainless pigeon follows with its head the lighted candle: its nerve of sight is therefore capable of taking part in the creation of a reflex movement. The same bird will eat largely when appropriate food is placed in its mouth--an indication that the nerve of taste is also active. In a word, to the middle brain the nerves of sight, of hearing, of tasting, of smelling, as well as those of common sensibility, bear impulses which find their appropriate nerve-centres and give origin to complicated reflex movements. Partly in the number and variety of the afferent nerves, and partly in the number and variety of the nerve-centres crowded into the lower brain, lie the causes of the great intricacy of the automatic movements which originate in this region. Of all the acts performed by the brainless frog, fish, bird or mammal, the most difficult to understand are those connected with standing, jumping, swimming, walking, flying, running, etc.; or, in other words, with equilibration, or the function of maintaining the equilibrium. Why does the brainless frog, the automaton, shift his position as the board upon which he sits is slowly tilted? There are apparently no new contacts of the skin: the motion is so quiet, so gentle, that it would seem as if there was nothing to produce irritation of the surface of the body so as to cause reflex acts. If it be true, as is asserted by some observers, that taking off the skin of the legs of the frog (a procedure which causes no pain, as the frog has no consciousness) prevents his shifting himself to maintain his equilibrium when his resting-place is moved, it is plain that the surface-irritations which cause the reflex alterations of position in the brainless frog originate in the skin of the legs and through the sense of touch. There are, however, certain facts which indicate that the impulses under discussion are not of so simple a character.