THE EARTH THE ABODE OF LIFE 



charged with mineral salts and accumulations that a 

 bather cannot sink in it, and will emerge from his bath 

 encrusted with salty deposits. As the early ocean 

 became more and more saturated (with lime and car- 

 bonates, etc.), the more vigorous of the living forms 

 in the water began to resist the change in various ways. 

 They tried to meet it, or to alter themselves so as not 

 to be incommoded by it. 



This is a very familiar occurrence in natural life and 

 evolution. Perhaps the commonest example of it that 

 we can select is the formation of corns on the human 

 feet and hands. A corn, properly considered, is the 

 defence raised by the skin against unusual or discom- 

 moding pressure or friction. When a boot is too tight, 

 or when a plough handle or a cricket bat or a golf 

 club is continually clasped tightly, a " callosity " or 

 horn-like defence is formed. In some cases a blister 

 is antecedent to the corn; and we may regard this not 

 only as showing the need for the hardening of the skin, 

 but as being a stage preliminary to it. There are many 

 other instances. Hair is formed as a protection to the 

 body, and owing to nature's economies is not usually 

 formed when clothing takes its place or heat renders 

 it unnecessary. If the heat is too great, or the light 

 beating on the unprotected skin is too strong, then 

 another form of protection takes the place of hair. 

 Why is it that races living near the Equator wear 

 "the burnished livery of the burning sun," and show 

 black or brown pigmentation of the skin ? It is 

 because this pigmentation arrests the penetration of 



"5 



