6 BRITISH LIZARDS 



their future, their association. This is the aspect 

 of Evolution, which includes the study of the most 

 fascinating portion of biology, and is largely a theo- 

 retical study as well as a practical one. It does not 

 refer to an individual, but to a group of individuals. 

 We do not speak of the evolution of a horse, but that 

 of the horse regarded as a species of animal. 



Thus we see that there are more aspects of an 

 animal that must be taken up in order to get a 

 complete description of it than we might suppose at 

 first sight. It is practically impossible for any one 

 man to make himself familiar with all that is known 

 of all these aspects even for a very few animals. 

 Each aspect is a study so far-reaching in itself that 

 one is more than most of us can manage to learn 

 thoroughly. But it is of the greatest importance to 

 remember that in describing an animal all these points 

 of view must be considered before a complete descrip- 

 tion has been given. 



For outdoor work the Physiological, the Geographical^ 

 and the Sioecific characters are the most important 

 aspects. Structure must not be lost sight of, for on 

 that alone do naturalists classify animals, but it is 

 studied here more in its relation to function than for 

 its own sake. The main questions the field naturalist 

 has to study are : — What animals live in a given 

 region ? What characters make them the species they 

 are ? How are they related to other living or extinct 

 forms ? How do they live their life ? 



