Habits and Adaptations 249 



sea-horse now uses his tail to grasp stems of seaweed, whereas 

 it was once as much an organ of locomotion as mammals' 

 paws. 



This particular adaptation is a protective one. It helps the 

 sea-horse to shelter itself among the weeds. In general, 

 adaptations help animals to survive. Fish must have oxy- 

 gen, food, mates, and, in most species, shelter from enemies. 



Figure 27. SEA-HORSE 



in order to live. It is probably safe to say that these require- 

 ments are to be found in greatest abundance in the shallow 

 parts of the ocean. Why did not all fish congregate there 

 and stay there? Why have they moved into the open seas, 

 into the cold black abyssal depths, ihto tide-pools above low- 

 water markj into rivers and mountain-streams, and swamps 

 that dry up 5 into lightless caves and artesian waters; into 

 pools that stagnate, into muddy roadside ditches, into rice- 

 fields flooded only part of the year j even into thermal springs 

 in such desert regions as Death Valley, where the water 

 temperature rises to 100 degrees Fahrenheit? 



Competition is the answer. Competition drove human be- 

 ings out of settled countries into new lands where new meth- 



