90 THE STORY OF LIFE IN THE SEAS. 



together in a tall jar of water, the former will 

 reach the bottom long before the latter. Simi- 

 larly the body of an animal which possesses a 

 dense armature of spines, as it presents more 

 surface to the water, sinks much more slowly 

 than the body of an animal of the same weight 

 that is smooth and compact. 



The spininess or hairiness of the Copepod body, 

 then, may be regarded as one of its adaptations 

 to the environment in which it lives. But of 

 course this character is not by any means con- 

 fined to the Copepods. Very many of the sur- 

 face-swimming Crustaceans, and more particularly 

 their larvae, have remarkably spiny bodies, and 

 among many of the Foraminifers, Kadiolarians, 

 Worms, Molluscs and even Fish we find some 

 similar extension of the surface of the body 

 which lowers the sinking rate. Another means 

 by which the bodies of many of the animals com- 

 posing the Plankton are buoyed up, is the secre- 

 tion into a special chamber or reservoir of some 

 gas or oil of a lesser weight than the sea- water. 

 This is what may be called the balloon principle. 

 In such animals we may regard the heavy 

 muscles, skeleton, skin and viscera as the car 

 and the freight of the balloon, while the gas 

 reservoir corresponds to the whole silk case con- 

 taining the coal-gas. 



Such an animal might also be compared to a 

 man in the sea clinging to an india-rubber life- 

 belt. The body of the man by itself is heavier 

 than the water, and in the absence of the muscular 

 exercise of swimming sinks rapidly to the bottom; 

 but the body of the man and the life-belt taken 



