: it establishes in the whole living world a vast resemblance which can be arranged in a scale of decreasing complexity, from man down to the zoophyte; in the higher species all these functions are present; but as we move down the scale, so we see them disappear one after the other, until finally, in the zoophyte, there is 'no centre of circulation, no nerves, no centre of sensation; each point seems to feed itself by suction'.