432 THE CAUSES OF THE XI 



parts of Bengal, into the dry, cold, bitter steppes 

 of Siberia, into a latitude of 50, so that they may 

 even prey upon the reindeer. These tigers have 

 exceedingly different characteristics, but still they 

 all keep their general features, so that there is no 

 doubt as to their being tigers. The Siberian 

 tiger has a thick fur, a small mane, and a longi- 

 tudinal stripe down the back, while the tigers of 

 Java and Sumatra differ in many important re- 

 spects from the tigers of Northern Asia. So lions 

 vary ; so birds vary ; and so, if you go further back 

 and lower down in creation, you find that fishes 

 vary. In different streams, in the same country 

 even, you will find the trout to be quite different 

 to each other and easily recognisable by those who 

 fish in the particular streams. There is the same 

 differences in leeches ; leech collectors can easily 

 point out to you the differences and the peculiari- 

 ties which you yourself would probably pass by ; 

 so with fresh-water mussels ; so, in fact, with every 

 animal you can mention. 



In plants there is the same kind of variation. 

 Take such a case even as the common bramble. 

 The botanists are all at war about it ; some of 

 them wanting to make out that there are many 

 species of it, and others maintaining that they are 

 but many varieties of one species ; and they can- 

 not settle to this day which is a species and which 

 is a variety ! 



So that there can be no doubt whatsoever that 



