200 THE HAUNTS OF LIFE 



NEW WAYS OF BREATHING 



The colonisation of the dry land by aquatic 

 animals cannot have been an easy task, and 

 our question now is: What were the neces- 

 sary qualifications? 



The first qualification was ability to capture 

 the oxygen of the dry air. There is a much 

 larger proportion of oxygen in the air than 

 there is mixed with the water, but it is not so 

 readily available. For, mixed with the water, 

 it seems to seep in very readily through the 

 delicate moist skin of the general surface of 

 the body, or of special organs, such as gills. On 

 one side of the membrane there is water, with 

 oxygen mixed in it; on the other side of the 

 membrane there is blood, which usually car- 

 ries a pigment with a strong affinity for oxy- 

 gen. What happens in aquatic breathing is that 

 the oxygen diffuses through the skin into the 

 blood, usually entering into a loose, chemical 

 union with the blood-pigment. With its cap- 

 tured oxygen the blood passes to the living tis- 

 sues of the animal, to the muscles, for instance, 

 and there surrenders its oxygen to keep up the 

 ceaseless burning (or oxidation) which living 

 implies. As the result of the combustion (or 



