Life of the Waters 357 



tion of two animals of the same species seeing and recognizing 

 one another; but of one species finding its' prey and another 

 escaping from its enemies ; while in many cases light produc- 



THE PORTUGUESE MAN OF WAR, AN ANIMAL ' ' U-BOAT ' ' 

 The balloon-like float filled with gas secreted by its walls floats at the 

 surface of the sea, so that the colony is carried hither and yon by wind 

 and tide. Each of the thread-like processes pendent from the float is 

 an individual member of the colony having its own special function to 

 perform, some having stinging cells for capture of prey, others serving 

 as feelers and still others as feeders, the mouths and stomachs of the 

 colony. By contraction of the float the gas is expelled and the animal 

 can submerge. A southern form, it is often carried by the Gulf Stream 

 into the North Atlantic. 



Courtesy of the American Museum of Natural History. 



tion may be purely incidental to other processes in the life 

 of the animal. And further, the same ends are attained in 

 different ways in different species. Nature knows "more 



