220 THE FOUNDATIONS OF ZOOLOGY 



Broadly stated, the history of each great line has been like that 

 of the echinoderms and brachiopods. The oldest pteropod or 

 lamellibranch or echinoderm or crustacean or vertebrate which we 

 know from fossils exhibits its own type of structure with perfect 

 distinctness, and later influences have done no more than to expand 

 and diversify the type, while anatomy fails to guide us back to the 

 point where these various lines met each other in a common source, 

 although it forces us to believe that the common source once had 

 an individual existence. Embryology teaches that each line once 

 had its own representative at the surface of the ocean, and that 

 the early stages in its evolution have passed away and left no record 

 in the rocks. 



If we try to call before the mind a picture of the land surface 

 of the earth we see a vast expanse of verdure stretching from high 

 up in the mountains over hills, valleys, and plains, and through 

 forests and meadows down to the sea, with only an occasional lake 

 or broad river to break its uniformity. 



Our picture of the ocean is an empty waste, stretching on and 

 on with no break in the monotony except now and then a flying- 

 fish or a wandering sea-bird or a floating tuft of sargassum, and 

 we never think of the ocean as the home of vegetable life. It 

 contains plant-like animals in abundance, but these are true ani- 

 mals and not plants, although they are so like them in form and 

 color. At Nassau, in the Bahama Islands, the visitor is taken in 

 a small boat, with windows of plate glass set in the bottom, to 

 visit the " sea-gardens " at the inner end of a channel through 

 which the pure water from the open sea flows between two coral 

 islands into the lagoon. Here the true reef corals grow in quiet 

 water, where they may be visited and examined. 



When illuminated by the vertical sun of the tropics and by 

 the light which is reflected back from the white bottom, the pure, 

 transparent water is as clear as air, and the smallest object forty 

 or fifty feet down is distinctly visible through the glass bottom of 

 the boat. 



As this glides over the great mushroom-shaped coral domes 

 which arch up from the depths, the dark grottoes between them 

 and the caves under their overhanging tops are lighted up by the 

 sun, far down among the anthozoa or flower animals and the 



