162 THE OCEAN 



have an example of one of the many existing 

 nutritive chains in the ocean : all the organic 

 matter elaborated in the bodies of these organ- 

 isms is, after death, attacked by bacteria, 

 and broken down to ammonia, nitrites, and 

 nitrates to form the food of the pelagic algae, 

 thus carrying on this cycle of anabolism and 

 katabolism. 



Influence of Temperature. — In Arctic and 

 Antarctic regions, when tow-nets are drawn 

 through the ocean waters, vast numbers of 

 crustaceans — schizopods, copepods and amphi- 

 pods — are captured which belong to relatively 

 few genera and species. When tow-nets are 

 drawn through tropical waters, they usually 

 capture similar pelagic creatures, but while 

 the quantity of organic matter in them is much 

 less than in the polar seas, the numbers of 

 genera and species greatly exceed those found 

 in the cold waters toward the north and south. 

 This contrast is apparently to be accounted 

 for by the rate of metabolism in the organisms, 

 to which reference has just been made. It 

 seems evident that the organisms captured 

 in the cold polar waters are of very different 

 ages, eggs and young and adults being found 

 at all seasons in the same hauls ; some of 

 these adults may be ten, twenty, or more years 

 of age. The actions of enzymes, of bacteria, 

 and of putrefaction are all slowed down in the 



