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.
The individuals composing one of these Siphonophora are so manifestly analogous to organs, that their individuality may, perhaps, be disputed, the more so as they do not live separately. But the gradations of separation are very fine. You would never hesitate to call a bee, or an ant, an individual, yet no bee or ant could exist if separated from its colony. So great is “the physiological division of labour,” which has taken place among these insects, that one cannot get food, another cannot feed itself, but it will fight for the community; another cannot work, but it will breed for the community; another cannot breed, but it will work. Each of these is little more than separated organs of the great insect-Organism; as the heart, stomach, and brain are united organs of the human-Organism. Remove one of these insects from the community, and it will soon perish, for its life is bound up with the whole.
And so it is everywhere; the dependence is universal:—
“Nothing in this world is single;
All things, by a law divine,
In one another’s being mingle.”
We are dependent on the air, the earth, the sunlight, the flowers, the plants, the animals, and all created things, directly or indirectly. Nor is the moral dependence less than the physical. We cannot isolate ourselves if we would. The thoughts of others, the sympathies of others, the needs of others,—these too make up our life; without these we should quickly perish.
It was a dream of the youth Cuvier, that a History of Nature might be written which would systematically display this universal interdependence. I know few parts of biography so interesting as those which show us great men in their early aspirings, when dreams of achievements vaster than the world has seen, fill their souls with energy to achieve the something they do afterwards achieve. It is, unhappily, too often but the ambition of youth we have to contemplate; and yet the knowledge that after-life brought with it less of hope, less of devotion, and less of generous self-sacrifice, renders these early days doubly interesting. Let the abatement of high hopes come when it may, the existence of an aspiration is itself important. I have been lately reading over again the letters of Cuvier when an obscure youth, and they have given me quite a new feeling with regard to him.
There is a good reason why novels always end with the marriage of the hero and heroine: our interest is always more excited by the struggles, than by the results of victory. So long as the lovers are unhappy, or apart, and are eager to vanquish obstacles, our sympathy is active; but no sooner are they happy, than we begin to look elsewhere, for other strugglers on whom to bestow our interest. It is the same with biography. We follow the hero through the early years of struggle with intense interest, and as long as he remains unsuccessful, baffled by rivals or neglected by the world, we stand by him and want him to succeed; but the day after he is recognized by the world our sympathy begins to slacken.