104 



THE STORY OF LIFE IN THE SEAS. 



surface to the water in proportion to its weight, 

 and consequently sinks slowly ; and secondly, 

 the protoplasm is provided with numerous 

 vacuoles containing a watery fluid, and in many 

 cases at least one larger vacuole containing oil. 

 If the liquids in these vacuoles are lighter than 

 sea-water, and there is good reason to suppose 



that some at least 

 of them are, then 

 they are of the same 

 nature as the oil 

 chambers of the 

 Copepods, and are 

 hydrostatic in func- 

 tion. 



Among the Fora^ 

 minifers very few 

 genera strictly be- 

 long to the surface 

 Fauna. Most of 

 them have heavy, 

 compact shells of 

 carbonate of lime, 

 and they live among 

 the sand or the rocks 

 at the bottom of the 

 sea. The best known 



of the surface-dwelling forms is Globigerina, and 

 this, in accordance with its habits, possesses a 

 shell which, like that of the Radiolarians, is very 

 light, perforated by numerous large holes and 

 provided with long delicate spines. The shell 

 of Globigerina might well be mistaken for that 

 of a Eadiolarian were it not for the fact that 



FIG. 29. 



Shells of Foraminifers living at the 

 bottom of the sea. 



