II 



THE INFLUENCE OF ENVIRON- 

 MENT ON THE STRUCTURE 

 AND HABITS OF ANIMALS 



I PROPOSE to ask your attention for a short time 

 to the consideration of the dependence of any 

 body, living or dead, organised or unorganised, 

 organic or inorganic, on its environment, i.e., on 

 the external conditions surrounding and acting on 

 it at a given time, and I propose to consider this 

 more especially with regard to animals. 



Of environment, as affecting inanimate objects, 

 many admirable examples are afforded us by Physics. 

 For instance, we speak of water as a definite sub- 

 stance having a definite existence, but we know well 

 enough that for the existence of water as such 

 certain definite relations of temperature and pres- 

 sure are essential. At the normal pressure water 

 will not exist as water at a temperature below o C. 

 Similarly, if we raise the temperature beyond a 

 certain limit, 100 C., the existence of water as 

 water again becomes impossible. If we alter the 

 pressure the relations change again, for when the 



