We take it, then, as proven that the colour sense does exist, at least, in all creatures possessing eyes. But there are myriads of animals revelling in bright tints; such as the jelly-fishes and anemones, and even lower organisms, in which eyes are either entirely wanting or are mere eye-specks, as will be explained in the sequel. How these behave with regard to colour is a question that may, with propriety, be asked of science, but to which, at present, we can give no very definite reply. Still, certain modern researches open to us a prospect of being able, eventually, to decide even this obscure problem. The question, however, is not a simple one, but involves two distinct principles; firstly, as to how colour affects the animal coloured, and, secondly, how it affects other animals. In other words, How does colour affect the sensibility of its possessor? and how does it affect the sense organs of others? To endeavour to answer the first question we must start with the lowest forms of life, and their receptivity to the action of light; for, as colour is only a differentiation of ordinary so-called white light, we might _a priori_ expect that animals would show sensibility to light as distinguished from darkness, before they had the power of discriminating between different kinds of light. This appears to be the case, for Engelmann has shown[9] that many of the lowest forms of life, which are almost mere specks of protoplasm, are influenced by light, some seeking and others shunning it. He found, too, that in the case of _Euglena viridis_ it would seek the light only if it "were allowed to fall upon the anterior part of the body. Here there is a pigment spot; but careful experiment showed that this was not the point most sensitive to light, a colourless and transparent area of protoplasm lying in front of it being found to be so." Commenting upon this Romanes observes, "it is doubtful whether this pigment spot is or is not to be regarded as an exceedingly primitive organ of special sense." Haeckel has also made observations upon those lowest forms of life, which, being simply protoplasm without the slightest trace of organization, not even possessing a nucleus, form his division _Protista_, occupying the no-man's-land between the animal and vegetable kingdoms. He finds that "already among the microscopic Protista there are some that love light, and some that love darkness rather than light. Many seem also to have smell and taste, for they select their food with great care.... Here, also, we are met by the weighty fact that sense-function is possible without sense organs, without nerves. In place of these, sensitiveness is resident in that wondrous, structureless, albuminous substance, which, under the name of protoplasm, or organic formative material, is known as the general and essential basis of all the phenomena of life."[10]