CHAPTER XV. 



WHAT IS EVOLVED IN EVOLUTION ?— INTRINSIC AND 

 EXTRINSIC CHARACTERS. 



Laws of Evolution indicated by History of Brachiopods We 



have now gained a sufficient knowledge of the characters of 

 Brachiopods to enable us to consider the question, What is 

 indicated regarding the laws of organic history by these facts? 



It is evident, first, that the history exhibits evolution. 

 Evolution of what ? We have been considering the time re- 

 lations of the genera in families of Brachiopods: is it evolu- 

 tion of genera ? Tables have been given of the phylogenetic 

 relations of the families of hinged Brachiopods: have we 

 been considering the evolution of families ? 



Before taking up these points a few words may be said 

 on the question, "What is evolved?" In general, we may 

 say, the history of organisms reveals a progressive evolution 

 of the viorpJiological characters which distinguish the succes- 

 sive organisms. Classes, orders, families, and genera are not 

 the things which are evolved. These are names for the 

 divisions of the classification we make of the evolved or- 

 ganisms. The classification, when historically considered, 

 expresses the evolution ; but the things classified are the indi- 

 vidual organisms, each of which has its characters distributed 

 through all the whole range of categories of the classification. 

 Therefore it is incorrect to speak of the evolution of one or 

 other of the categories — as a species or a genus: it is this or 

 that character of the individual that was acquired by evolu- 

 tion, as contrasted with other characters acquired by natural 

 generation from its parents. 



Mag-ellania Flavescens Examined as an Illustration. — In illus- 

 tration of this proposition we may take, for instance, a Magcl- 



26 c 



