2 FOOT-NOTES TO EVOLUTION. 



published by Linnaeus in 1758. This book treats of all 

 the species of animals known a century and a half ago. 



In its eight hundred and twenty-three 

 The number of , ^, j j-rr ^i- j 



pages some four thousand different kmds 

 species. ^ ° 



of animals are named and described. 

 But for every one of these enumerated by Linnaeus, more 

 than two hundred kinds are known to the modern natu- 

 ralist, and the number of species still unknown doubt- 

 less exceeds that of those already recorded. Every year 

 since 1864 there has been published in London a plump 

 octavo volume known as the Zoological Record. Each 

 of these volumes, larger than the whole Systema Naturae, 

 contains the names of animals new to science added to 

 our list during the year of which it treats. And in the 

 record of each year we find the names of about three 

 times as many animals as are mentioned in the Systema 

 Naturae. Yet the field shows no signs of exhaustion. 

 As these volumes stand on the shelf together it is easy 

 to see that the later volumes are the thickest, and that 

 the record for the present year is the largest of all. 

 Moreover, what is true of the increase of knowledge in 

 systematic zoology is even more marked in the case of 

 botany. Such, then, is the variety of life on the globe 

 — a variety of which Linnaeus and his successors had 

 never dared to dream. 



And yet, great as this variety is, there are, after all, 

 only a few types of structure among all animals and 



plants, some three or four or eight or 



The unity of . 1 j r j i . j 



•' ten general modes of development, and 



all the rest are modifications from 

 these few types. It is, moreover, true that all living 

 forms are but series of modifications and extensions of 

 one single plan of structure. All have the same frame- 

 work of cells, and in each cell we find the same ultimate 

 substance — the mysterious semi-fluid network of proto- 



