PROTOZOA 



183 



FIG. 212. Photograph of human red blood corpus- 

 cles two of which contain the malarial parasite. 

 Enlarged one thousand times. 



Chalk formers. 



The Globigerince 



are among the most 



abundant protozoa 



in the sea. Nearly 



all surround them- 

 selves with a shell 



of soft calcium car- 

 bonate (chalk). A 



pint of ocean water 



in the warmer 



climes may contain 



millions of them. 



The shells of the 



dead dropping to 



the bottom of the ocean have formed a thick layer of ooze 



over much of the ocean bed. The great chalk cliffs in 

 England, and the chalk beds 

 in Ireland, Denmark, Central 

 Europe, North Africa, Syria, 

 Central Asia, Texas, Kansas, 

 and South Dakota are com- 

 posed almost entirely of the 

 shells of GlobigerinaB that lived 

 ten millions of years ago or 

 more. The small piece of chalk 

 used by the carpenter is made 

 of millions of the skeletons of 

 these tiny protozoans. 

 The protozoa were no doubt 



FIG. 213. Shell of Globigerina. r 



Photograph enlarged forty diameters, the first animals On earth, 



