Page:Popular Science Monthly Volume 53.djvu/640

620 will manage to procure the capital required for its purchase and for running the railroads. It will be especially interesting to see whether it will be able to keep the promises that have been made in its name, and to compare private management under the control of the state with direct management by the state in a democratic country.—Translated and abridged for the Popular Science Monthly from the Musée Social.



ROM the simplest plant to the heart and brain of the world's-L chief denizen the organic kingdoms are the prey of a myriad parasites. These are outsiders and insiders, living in or upon the skin of their host, or burying themselves in its cavities and tissues, bones and vital organs. They are strongest and most numerous in the lower species, which can offer least resistance. If the Epizoa are sometimes accidentally useful, the class as a whole is injurious. But they are not less destructive to themselves. They sink in the scale of being through atrophy of their parts till they are no longer recognizable. What is the sociological significance of this strange blot on the face of Nature? It has been ingeniously suggested that parasitism is the insurrection of the vanquished lowest species against the higher species that have supplanted them in the possession of the earth; and the view may be found as philosophical as it is picturesque.

Commensalism arises when, besides living by their means, if no longer at their cost, the inferior species render a service to the superior. Certain crustaceans eat the excrement of fishes, and thus purify the water. One species of birds hunts parasites in the crocodile's throat, another clears the elephant's back of them. The scavenger vulture and hyena banquet on the remains of the carnivore's feast. The struggle for existence between two species, direct in parasitism, is indirect in commensalism.

Rivalry gives place to coalition. Different species of birds ally for safety. The sentinel ostrich warns troops of gazelles, zebras, and quaggas. Conversely, the Abyssinian damon unconsciously protects the lizard and ichneumon. Mutualism is a prophecy of the coexistence of alien peoples.

These three types of relationship among animals—parasitism,