If the whole brain is removed from a vertebrate animal, the effect is always fatal. But whereas in man section of the spinal cord is followed by instantaneous death, the decapitated trunk no longer showing any reflex movements whatever, brainless animals (spinal animals) are well able to carry out such movements. This is the more true the lower the animal stands in the vertebrate series. In apes there are indications only of such movements. A spinal dog makes running movements when the under-surface of the paws is pressed. Its tail can be caused to wag. A decapitated rabbit makes one or two last jumping movements. Fowls and pigeons with their heads cut off run around with wings beating. In these spinal animals all complicated faculties have disappeared owing to the loss of all the higher centres and of the main sensory centres. But the co-ordination of normal locomotory movements persists because this depends on centres in the spinal cord. Lower vertebrates can be kept alive even longer after being deprived of their fore-brain. A spinal frog still plainly exhibits all reflexes. If the skin of such a frog is moistened with dilute acetic acid, the animal makes movements with the foot of the side touched, as if to remove the stimulus. If this extremity is prevented from moving, the frog uses the other leg in an apparently purposeful manner. This experiment proves that biologically useful actions can take place without the presence of consciousness. Such experi ments have the further value of showing which actions of animals can take place in an apparently purposeful fashion, but without any intervention of the highest centres, that is without conscious intention.
nation of important stimuli corresponds to a model or schema in the brain. The effects of such a stimulus-complex upon a par ticular group of sensory cells, for example the retinal elements upon which the separate points of the image of an object fall, are conducted by definite appropriate groups of nerve fibres, past the association neurones and the lower centres, until they arrive finally at the highest centres. There the sensory nerve paths reach their end-points. But these end-points must from the nature of things have some spatial arrangement. Von Uexkiill assumes that the impulses conveyed to these end-groups are transferred to the corresponding schema somewhat after the manner of elec trical induction. The stimulation of the schema then causes a particular reaction of the animal in a relatively simpler manner. The discrimination of spatial boundaries of objects by the most highly organized central nervous systems and brains thus requires a fixed spatial arrangement of nerve paths. The higher brains, as it were, reflect a portion of reality in their schemata through the spatial interrelationship of their parts. In this way there arises in the central nervous systems of the higher 'animals a new indi vidual universe. Von Uexkiill calls this the counter-world (Gegen welt). Although the things in the outside world which are impor tant to the animal may correspond to definite schemata, the spatial arrangement of the elements of the schema need not be identical with the spatial structure of these objects. And it cer tainly is not identical. The immense complication of structure of the highest centres which this discussion implies to be necessary must be the reason why reactions to form-stimuli only occur in animals possessed of well-developed and highly complex brains. But that this faculty may exist in relatively low animals is shown by the fact that hermit-crabs have been trained to use as dwell ings snail-shells of a particular shape only, and to shun other shells. It is evident, therefore, that these animals, through re sponses to stimuli in their nerve centres, must be able, then, to distinguish the shapes of these objects from one another.