usually spoken of as if they were convertible terms. That this is inexact may be readily shown, and that it is misleading appears in its causing physiologists to credit every ganglion, wherever found, with central functions; and, by an almost inevitable extension of the error, has led to the assignment of central functions to a single ganglionic cell! This is but part of that “superstition of the cell” against which I shall have to protest. I will not here raise the doubt which presses from various sides respecting the central functions of the ganglia in the heart and intestines, because the reader perhaps shares the general opinion on that point; but let me simply ask what central function can possibly be assigned to the ganglia on each of the spinal sensory nerves? above all to those grouped and scattered ganglionic cells which are found at the peripheral termination of some nerves, and in the very trunks of others? There may, indeed, be imagined a central function for the ganglia in the mesentery, and even in the choroid coat of the retina, on the hypothesis (quite gratuitous, I think) of their regulating the circulation; but even this explanation cannot be adopted with respect to the ganglionic cells which appear in the course of the nerve.[87] The meaning of a physiological centre is, that it is a point _to_ which stimulations proceed, and _from_ which they are reflected. The meaning of a ganglion is, that it is a group of nerve cells dispersed among, or in continuation with, nerve fibres: it may be a centre of reflection, or it may not; and in the latter case its physiological office is at present undetermined. A ganglion is no more a centre in virtue of its cell-group than a muscle is a limb. All function depends on connection, and central function demands a connection of afferent and efferent parts. 19. The ganglia found in the ventral cord of the Invertebrate (see Fig. 1) are centres, each of which has considerable independence, each regulating a single segment of the body, or a group of similar segments. As the scale of animal complexity ascends, these separated centres tend more and more to coalesce, and with this coalescence comes an increasing _combination_ of movements.[88] Observe the caterpillar slowly crawling over a leaf; each segment of its body moves in succession; but when this caterpillar becomes a butterfly the body moves rapidly, and all at once. Open the caterpillar, and you find its nervous centres are thirteen separate ganglia, each presiding over a distinct part of the body, and each capable of independent action. Open the butterfly, and you find the thirteen ganglia greatly changed: the second and third are fused into one; the fourth, fifth, and sixth into another; the eleventh and twelfth into another; the only trace of the original separation is in a slight constriction of the surface. The movements of the caterpillar were few, simple, slow, and those of the butterfly are many, varied, and rapid.