Internally again the principal interest of the organism is its extreme simplicity. There is no stomach or gut, no heart or veins, no lung or gills, no kidneys and no brain. The animal is in fact a simple sac, the inner walls are much folded to increase their area, but there is but one body-space to serve for everything. In this space the food is digested. There is but one opening into it from the outside, so the indigestible remnants of the food are voided by the same opening as that they entered by. Simplicity of organisation could scarcely go farther; we have here an example of one of the lowest forms of life. Lowly organisms of this kind shew an astonishing indifference to the separation of one part from another. No cutting or mutilation does any permanent harm. Chop the beast to fragments, and not only will each piece remain alive, but it will grow until it encloses a new sac, forms a new mouth, tentacles, and adhesive base, and behold a number of new and complete polyps. This possibility has been taken advantage of by nature, and numbers of these lowly forms of life propagate themselves in this way. A projection arises on the side of the animal, is automatically amputated, grows missing organs, and becomes a complete and independent animal. The process is exactly like the planting of rose-cuttings, one of the cases of asexual reproduction in the animal kingdom. Now in many cases, where propagation by buds takes place, the buds undergo their full development into complete polyps while remaining connected with the parent. An example of a “colony” of sea-anemones thus formed is given by Plate XXV, Figs. 53 and 54. An allied form, known as _Palythoa_, is common in the Red Sea as little star-like rings of tentacles, of a beautiful deep, yet bright, green, carpeting the sand and stones in shallow water. Each star, or polyp head, measures about a quarter-inch in diameter, so that when a few dozen occur together they form a quite conspicuous patch of colour. As already stated the corals are similar “colonial” organisms, the numerous cups on their stony branches representing each one polyp head. But how the polyps are connected with the stony material is best explained by, as before, taking the simplest possible case, that of a solitary non-colonial polyp, which is exactly like our simple sea-anemone, but has a stony cup like one of those of the ordinary corals.