Land-Birds in the Philippines. 419 



Melanopitta sordida occurs alone through most of the islands, 

 but with M. steerii in Mindanao and Samar ; also that the 

 large Megalurus palustris alone occupies the northern and 

 western islands, the smaller M. rujiceps the central islands, 

 while the two species inhabit Marinduque together. 



It seems probable that Melanopitta and Tanygnathus are 

 cases in which two species of a genus, after having originated 

 in different areas, have been brought together when differing 

 just too much to fuse, while they still remain almost identical 

 in habits and food, and so are brought into such conflict that 

 the Aveaker species is disappearing. 



Putting lists B and C together, there are 128 genera out of 

 151, and 228 species out of 316, in which each genus is repre- 

 sented by only a single species in a locality. This is about 

 thirteen fifteenths of the whole number of genera and five 

 sevenths of the whole number of species — altogether too great 

 a proportion of both to have no significance. 



If to lists B and C we add list D, there result 145 genera 

 out of 151, and 305 species out of 316, or twenty-nine in 

 every thirty of the genera and over thirty in every thirty- 

 one of the species, so distributed in the islands that no two 

 species nearly enough allied to be put in the same section or 

 subgenus are found existing in the same island. 



These three lists teach the same law of distribution, and 

 the difficulty in formulating it lies not in the facts but in the 

 necessary imperfection of the terms used in measuring the 

 values of the various natural groups of animals. The fact that 

 these natural groups differ in value indefinitely makes it for 

 ever impossible to so measure them by the fixed rule of species 

 and genus that all men shall agree to the results. 



The law of distribution of non-migratory land-birds of the 

 Philippines may be stated as follows : — 



Every genus is represented by only a single species in one 

 place. 

 Or, in more general terms, as follows : — 



No two species structurally adapted to the same conditions 

 will occupy the same area. 



The varieties or subspecies of birds in the Philippines, 

 wherever observed, follow the same law of distribution as the 



