Adaptations of Fishes 2 1 5 



and reefs of the tropical seas. About the coral reefs is the center 

 of fish competition. A coral archipelago is the Paris of fishes. 

 In such regions is found the greatest variety of surroundings, 

 and therefore the greatest number of possible adjustments. 

 The struggle is between fish and fish, not between fishes and 

 hard conditions of life. No form is excluded from the com- 

 petition. Cold, darkness, and foul water do not shut out com- 

 petitors, nor does any evil influence sap the strength. The 

 heat of the tropics does not make the sea- water hot. It is 

 never sultry or laden with malaria. 



From conditions otherwise favorable in arctic regions the 

 majority of competitors are excluded by their inability to bear 

 the cold. River life is life in isolation. To aquatic animals 

 river life has the same limitations that island life has to the 



FIG. 157. Skeleton of the Cow-fish, Lactophrys tricornis (Linnseus). 



animals of the land. The oceanic islands are far behind the 

 continents in the process of evolution in so far as evolution im- 

 plies specialization of parts. In a like manner the rivers are 

 ages behind the seas, so far as progress is concerned, though 

 through lack of competition the animals in isolation may be 

 farthest from the original stock. 



Therefore the influences which serve as a whole to intensify 

 fish life, to keep it up to its highest effectiveness, and which 

 tend to rid the fish of every character or structure it cannot 

 "use in its business," are most effective along the shores of the 

 tropics. One phase of this is the retention of low numbers of 

 vertebrae, or, more accurately, the increase of stress on each 

 individual bone. 



Conversely, as the causes of these changes are still in opera- 



