Let us pass from the coral to the stem of some other polype, say a Campanularia. Here is the representation of such a stem, of the natural size, and beside it a tiny twig much magnified. You observe the ordinary polype issuing from one of the capsules, and expanding its coronal of tentacles in the water. The food it secures will pass along the digestive tract to each of the other capsules. Under the microscope, you may watch this oscillation of the food. But your eye detects a noticeable difference between this polype in its capsule, and the six semi-transparent masses in the second capsule: although the two capsules are obviously identical, they are not the same: a _differentiation_ has taken place. Perhaps you think that six polypes are here crowding into one capsule? Error! If you watch with patience, or if you are impatient yet tolerably dexterous, you may press these six masses out, and then will observe them swim away, so many tiny jelly-fish. Not polypes at all, but jelly-fish, are in this capsule: and these in due time will produce polypes, like that one now waving its tentacles. Having made this observation, it will naturally occur to you that the polype stem which bore such different capsules as are represented by these two, may perhaps be called a colony, but it is a colony of different individuals. While they have all one skeleton in common, nutrition in common, and respiration in common, they have at least one differentiation, or setting apart for a particular purpose, and that is, the reproductive capsule. This is an individual, as much as any of the others, but it is an individual that does nothing for the general good; it takes upon itself the care of the race, and becomes an “organ” for the community; the others feed it, and it is absolved from the labour of nutrition, as much as the arm or the brain of a man are. From this case, let us pass to the group of jelly-fish called _Siphonophora_ (siphonbearers) by naturalists, and we shall see this union of very different individualities into one inseparable colony still more strikingly exhibited: there are distinct individuals to feed the colony, individuals to float it through the water, individuals to act as feelers, and to keep certain parts distended with fluid, and finally reproductive individuals. All these are identical in origin, and differ only by slight differentiations.[7] Here we have obviously an approach to the more complex organism in which various distinct organs perform the several functions; only no one calls the Organism a colony.