a fraction of the nerve-cord, separated by severances in front and behind, is left, corresponding with a single abdominal segment, the rhythmic action of that segment continues; but it is no longer synchronous with that of adjacent segments similarly isolated. It will probably not be contended that the co-ordinated rhythm of the isolated segment in crayfish or king-crab is anything but a bit of organic and physiological behaviour. Whether it be accompanied by consciousness--a bit of consciousness isolated from other bits--we do not know; but we have no grounds for supposing that the rhythmic behaviour is guided by consciousness. And when, as Dr. Carpenter pointed out half a century ago, a water-beetle, from which the “brain” has been removed, swims forwards if placed in water, we must surely regard the co-ordinated progression as organic behaviour, whatever view we may hold with regard to a consciousness which in such a case is in a very literal sense a divided consciousness. In these invertebrates the central nervous system is obviously segmented--one can distinguish the ganglia and their connecting nerve-strands. In the vertebrate the brain and spinal cord form a continuous mass of nerve-tissue without obvious segmentation. But the pairs of spinal nerves, each nerve with its afferent and efferent “root,” indicate a really segmented condition, though in the cord itself the segments so run together and overlap that they cease to be externally obvious. And there is a certain, though limited, amount of overlap in the distribution of these segmental nerves. Still, well co-ordinated responses occur when comparatively short portions of the spinal cord are isolated by severance from the rest. In the male frog, especially during the breeding season, a clasping reflex is produced by stimulating the dark swollen pads on the inner side of the hand, and this, as Goltz has shown, is exhibited when all the central nervous system has been destroyed save the segments to which the nerves for the arms proceed. “Similarly,” writes Dr. Sherrington,[190] “in the cat and monkey, the reflex wagging of the tail persists when behind the spinal transection only the sacral region of the cord is left intact.” When the spinal cord of the dog is severed, so as to isolate that portion which is concerned with movements of the hinder part of the body, pressure on the pad of one hind-foot usually produces, not only a lifting of that leg, but also an extension of its fellow--that is to say, a co-ordinated response of the two limbs. But in the case of the vertebrates, more than in that of the invertebrates, the co-ordinated response of an isolated part of the central nervous system seems to lack the furtherance of its action, which normally comes from the higher centres from which it has been severed. “The spinal reflexes significant of progression seem,” says Dr. Sherrington,[191] “to contribute chiefly towards preparatory posture in readiness for