THE DRAMA OF LIFE ii 



occurrence of about 462 difierent kinds of birds, and the 

 total number of living species of birds may be safely 

 estimated at not less than ten thousand. 



Dr. Gadow, writing in 1898, estimated the number of 

 recent species of Vertebrate animals at 24,241. He put 

 Mammals at 2,702, Birds at 9,818, Eeptiles at 3,441, Amphi- 

 bians at 925, Fishes at 7,328, and primitive Vertebrates 

 at 27. But it is when we pass to the Invertebrates that 

 the numbers of species mount up so enormously. Thus an 

 authority on Diptera has put the probable number of 

 species at a hundred thousand, and there is no doubt that 

 there are many times more species of insects than of all 

 other animals put together. Dr. Sharp remarks that 

 though the largest insects scarcely exceed in bulk a mouse 

 or a wren, ' yet the larger part of the animal matter existing 

 on the lands of the globe is in all probabihty locked up in 

 the forms of Insects '. 



The same authority estimates the number of named 

 species of insects at 250,000 ; and suggests that this is only 

 about a tenth of the total. It has been estimated that 

 there are about 200,000 plants, of which about a half are 

 Dicotyledonous Flowering Plants. But even more im- 

 pressive is Darwin's record of finding twenty species of 

 Flowering Plants in a patch of turf four feet by three ; 

 or the finding of four hundred in a square mile. 



Variety of Form. — There are not very many main styles 

 of architecture among animals, but there is endless variety 

 in detail. All the Vertebrates are obviously reducible to 

 one style of architecture, but what contrasts there are be- 

 tween eagle and whale, between tortoise and snake, between 

 eel and skate, between frog and newt, between swift and 

 penguin, between weasel and giraffe, between minnow and 



