TIIE SARCODIXA 



165 



As the animals die their shells sink to the bottonn, fornning the 

 " forarniniferal ooze " found at great depths in regions like the 

 North Atlantic CFig. 90). In spite of their small size, and the slow 

 rate at which they accumulate upon the bottom, such protozoan 

 skeletons have become a part of sedimentary rocks in the same 

 manner as the shells of larger animals. The chalk formations in 



Fig. 90. — .Shells of marine Foramiriifera. 



I>eft, foraminiferal ooze from bottom of ocean at 1900 fathoms. Right, piece of 

 nummulitic linieBtone, shouing {(jtaW ehella of the foraniiniferari Summulitft. 'From .Ship- 

 "ey, " Inverebrate Zix^logy," copyright, 1903, by A. and C. Black, reprinted by per- 

 luiiuiion.) 



various parts of the world, like tho.se of England and France, as .seen 

 in the chalk chffs of the English Channel, are composed almost 

 exclusively of the .shells of Foraminifera that once lived at the sur- 

 face of the ocean, died, and " rained " down upon the lx)ttom, to 

 be later con.solidated into rock and raised up as part of the dry 

 land, where they are now expo.sed as layers, .sometimes hundreds 

 of feet in thickness. Among the Actinopoda, two representative 

 types deser^-e mention: the " sun animalcules," hke Actinophrys 

 sol (Fig. 8.5 j, which is common in fresh wat€r; and the marine forms 

 known as Radiolaria, which are famous for their Vxjautiful .siUceous 

 skeletons. These, like the Poraminifera, have contributed to the 

 formation of sedimentary' rocks. 



In conclu.sion it may be remarked that the Sarcodina are 

 the simplest of the protozoa in their internal organization and 

 external differentiation. There are, however, rea.sons for believing 

 that they are less primitive, from an evolutionary .standpoint, than 

 the Mastigophora. Many of the Sarcodina, for example, have a 



