620 POPULAR SCIENCE MONTHLY. 



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 coun- 

 try. — Translated and abridged for the Popular Science Monthly 

 from the Musee Social. 



THE EYOLUTIOIT OF COLONIES. 



By JAMES COLLIER. 



III.— IMMIGRANTS AND INDIGENES. 



Ij^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 recog- 

 nizable. What is the sociological significance of this strange blot on 

 the face of IsTature ? It has been ingeniously suggested * that parasit- 

 ism 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 f)ic- 

 turesque. 



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 croco- 

 dile's throat, another clears the elephant's back of them. The scav- 

 enger vulture and hyena banquet on the remains of the carnivore's 

 feast. The struggle for existence between two species, direct in para- 

 sitism, is indirect in commensalism. 



Eivalry 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 co- 

 existence of alien peoples. 



These three types of relationship among animals — parasitism, 



* By M. Alfred Espinas. Societes animales, first edition, pp. 21, 22. 



