ANIMAL LIFE 163 



low temperature conditions. In tropical 

 waters, on the other hand, all these processes 

 are accelerated, and the various phases in the 

 life-history of these organisms are passed 

 through rapidly ; it is unlikely that any of 

 these minute organisms in tropical seas are 

 older than some days, weeks or months. It 

 is in this way that we may account for the 

 greater quantity of organic matter in cold 

 polar waters, which furnishes abundant food 

 for such huge animals as the whalebone whales. 

 The stomachs of these whales when killed are 

 sometimes found to be so crammed with 

 copepods and other crustaceans that they 

 may be dug out with a spade. In the equa- 

 torial waters the toothed whales feed, not on 

 these small plankton organisms, but on cuttle- 

 fish, fishes, and other large creatures. It is 

 also probable that this temperature relation 

 is correlated with the fact that in the cold polar 

 waters the individuals are many, while the 

 genera and species are few, and that in 

 tropical waters the individuals are relatively 

 few while the genera and species are many. 



Another peculiarity depending apparently on 

 temperature is the fact that the development 

 of a large number of polar marine animals 

 is direct. During the " Knight Errant " 

 Expedition in the Faroe Channel many 

 hundreds of holothurians (Lcetmogone violacea) 



