62 , THE HISTOEY OF CREATION. 



immense variety of forms, sometimes creeping at the bottom 

 of the sea, sometimes swimming on the surface. Only very 

 few live in fresh water (Gromia, Actinosphserium). Most of 

 them possess solid calcareous or flinty shells of an extremely 

 beautiful construction, which can be perfectly preserved in a 

 fossil state. They have frequently accumulated in such 

 huge numbers as to form mountain masses, although the 

 single individuals are very small, and often scarcely visible, or 

 completely invisible, to the naked eye. A very few attain 

 the diameter of a few lines, or even as much as a couple 

 of inches. The name which the class bears is given 

 because thousands of exceedingly fine threads of protoplasm 

 radiate from the entire surface of their naked slimy body ; 

 these rays are quasi-feet, or pseudopodia, which branch ofi' 

 like roots (whence the term Rhizopoda, signifying root- 

 footed), unite like nets, and are observed continually to 

 change form, as in the case of the simpler plasmic feet of 

 the Amoeboid ea, or Protoplasts. These ever-changing little 

 pseudo-feet serve both for locomotion and for taking food. 



The class of the Rhizopoda is divided into three different 

 legions, viz. the chamber-shells, or Acyttaria, the sun-animal- 

 cules, or Heliozoa, and the basket-shells, or Eadiolaria. The 

 Chamber-shells (Acyttaria) constitute the first and lowest of 

 these three legions ; for the whole of their soft body consists 

 merely of simple mucous or slimy cell-matter, or proto- 

 plasm, which has not difierentiated into cells. However, 

 in spite of this most primitive nature of body, most of the 

 Acyttaria secrete a solid shell composed of calcareous earth, 

 which presents a great variety of exquisite forms. In the 

 more ancient and more simple Acyttaria this shell is a 

 simple chamber, bell-shaped, tubular, or like the sheU of 



