114 PHYSIOGNOMY OF PLANTS. 



fish, 700 reptiles, 4000 birds, and 500 mammalia. Europe 

 has about 80 species of indigenous mammalia, 400 birds, 

 and 30 reptiles. In the Northern temperate zone, there- 

 fore, the species of birds are five times more numerous than 

 those of mammalia, as there are in Europe five times as many 

 Composite as there are Amentacese and Coniferae, and five 

 times as manyLeguminosse as there are Orchideae andEuphor- 

 biacese. In the southern hemisphere the ratio of mammalia 

 is in tolerably striking agreement, being as 1 to 4'3. Birds, 

 and still more reptiles, increase in the number of species 

 in approaching the torrid zone more than the mammalia. 

 Cinder's researches might lead us to believe that the pro- 

 portion was different in the earlier state of things, and that 

 many more mammalia had perished by revolutions of Nature 

 than birds. Latreille has shewn what groups of insects 

 increase towards the pole, and what towards the equator. 

 Illiger has given the countries of 3800 species of birds 

 according to the quarters of the globe : it would have been 

 much more instructive if the same thing had been done 

 according to zones. We should find little difficulty in 

 comprehending how on a given space of the earth's surface 

 the individuals of a class of plants or animals limit each 

 other's numbers, or how, after long continued contest and 

 many fluctuations caused by the requirements of nourish- 

 ment and mode of life, a state of equilibrium should be at 

 last established ; but the causes which have limited not the 

 number of individuals of a form, but the forms themselves, 

 in a particular space, and founded their typical diversity, are 

 placed beneath the impenetrable veil which still conceals 



