_Purple._ Eucrytidium, Acanthostratus. _Blue._ Cyrtidosphæra, Coelodendrum. _Green._ Cladococeus, Amphilonche. _Brown._ Acanthometra, Amphilonche. Examples of these may be seen in the plates of Haeckel's fine work, and as an illustration of regional decoration we cite _Acanthostratus purpuraceus_, in which the central capsule is seen to run from red to orange, and the external parts to be colourless, with red markings in looped chains. _Spongocyclia_ also exhibits this regional distinction of colour very clearly, the central capsule being red and the external portion yellow. The _Spongida_, or sponges, are, broadly speaking, assemblages or colonies of amoeba-like individuals, united into a common society. Individually the component animals are low, very low, in type, but their union into colonies, and the necessity for a uniform or common government has given rise to peculiarities that in a certain sense raise them even above the complex radiolaria. Some, it is true, are naked, and do not possess the skeleton that supports the colony, which skeleton forms what we usually call the sponge; but even amongst these naked sponges the necessity for communal purposes over and above the mere wants of the individual, raises them a step higher in the animal series. A multitude of individuals united by a common membrane, living in the open sea, it must have happened that some in more immediate contact with the food-producing waters, would have thriven at the expense of those in the interior who could only obtain the nutriment that had passed unheeded by the peripheral animals. But just as in higher communities we have an inflowing system of water and an out-flowing system of effete sewerage quite uncontrolled, and, alas, generally quite unheeded by the individuals whose wants are so supplied; so in the sponges we have a system of inflowing food-bearing water and an out-flowing sewage, or exhausted-water system. This is brought about by a peculiar system of cilia-lined cells which, as it were, by their motion suck the water in, bringing with it the food, and an efferent system by which the exhausted liquid escapes. These cilia-lined cells are the first true organs that are to be found in the animal kingdom, and according to the views we hold, they ought to be emphasized with colour, even though their internal position renders the colouration less likely. This we find actually to be the case, and these flagellated cells, as they are called, are often the seat of vividest colour.