172 THE STORY OF LIFE IN THE SEAS. 



of space, but because we possess so little posi- 

 tive information on the subject, which is of 

 greatest interest to us here, of their develop- 

 mental history. Lists of species infesting differ- 

 ent Fish and Whales could be published, a state- 

 ment of the points of anatomical importance 

 which distinguish the families could be written, 

 but they would present few features of interest 

 to the general reader. 



It may be well to point out before the chapter 

 is closed, however, that there is probably no 

 branch of our subject that is so little known 

 and presents such a wide and important field for 

 future investigation as the life-histories of these 

 marine parasites. 



CHAPTER VIII. 



THE ORIGIN OF THE MARINE FAUNA. 



WHEN we survey the distribution of living 

 organisms over the surface of the globe, we 

 cannot fail to be impressed with the enormous 

 range in the characters of the physical conditions 

 which are capable of supporting animal and 

 vegetable life. Thus we find Birds flying in the 

 sunlight of the cold and very light atmosphere of 

 the mountain tops, and Fishes swimming in the 

 chill darkness of the depths of the ocean, sup- 

 porting a pressure of two tons to every square 

 inch of their bodies. We find Algae, which give 

 the snow sometimes the name of " Red snow," 

 flourishing at temperatures below the freezing 



