146 



THE LIFE OF CRUSTACEA 



of the body with fluid acts in another way, by 

 increasing the surface exposed to friction with the 

 surrounding water, and so retarding sinking. The 



Fig. 50— The Zoea Larva of a Species of Sergestes, taken by 

 THE " Challenger " Expedition, x 25. (After Spence Bate.) 



principle involved is illustrated by the fact that a 

 soap-bubble sinks much more slowly through the 

 air than the drop of water into which it collapses. 



