Page:Popular Science Monthly Volume 33.djvu/597

Rh they may be numbered by hundreds or even thousands, form one continuous organism.

The stomach of each member of the colony is directly continuous with the hollow roots, and, through these, with the body of every other member, and any food which is captured and digested by one, serves to nourish all, since it circulates everywhere through the roots, as water flows through the mains to all the houses in a city.

The whole is the result of multiplication by buds, and all the members are derived from one, which hatched from an egg, and, fastening itself to a shell, founded a new colony. A new bud may grow out anywhere, from the roots, and as the current of food which is always sweeping by provides it with ample nourishment, it grows quickly, and the repetition of the process of budding brings about a rapid increase in the size of the community.

The existence of a mechanism for propelling food to all its members facilitates the division of labor, or polymorphism, which is the most remarkable characteristic of these hydroid communities. In human history the growth of agriculture has supplied the first need of all men, abundant food, by the labor of a few, and has thus rendered division of labor possible, and has permitted many persons to train and qualify themselves for many pursuits which do not contribute to the food-supply. The existence, among the hydroids, of a mechanism for feeding them independently of their own efforts, has permitted the same sort of specialization to grow up, and even to become more perfect in some respects than it is among mankind.

The welfare of any species requires that the individuals shall be supplied with food, protected from accidents and enemies, and enabled to reproduce the species, and while many parasitic animals, and the young of many others, are supplied with food without exertion, the conditions of their life do not usually permit much specialization, and this does not, as a rule, occur unless the individuals of the species form communities. The social ants and bees are divided into castes, and the existence of hydroid colonies, which are structurally united into compound organisms, presents the conditions which are most favorable for specialization among the members of the community. We accordingly find among them the most remarkable examples of division of labor, accompanied by structural specialization or polymorphism.

A young dysmorphosa colony consists of a creeping root, which carries a number of hydras, all of them like a in the figure. They are the eating and digesting members of the society. Each of them has a long tubular body, almost completely filled by a capacious stomach, which opens to the exterior, at the free end of