Protozoa. 



21 



FIG. 9. 



ules circulate actively in the body mass ; obscure con- 

 densed points or nuclei also exist, and the name of 

 the class is derived from the root-like spreading of the 

 pseudopodia. A few allied forms are shell-less. 



Mode of Growth of Rhizopoda. Those Rhizo- 

 pods that separate lime from the sea-water to form 

 shells, begin the process while they are young single 

 masses, and they increase by budding, each bud 

 forming on the newest 

 end of the last bud ; 

 consequently the per- 

 fect animal consists 

 of a rod-like or spiral 

 set of chambers, each 

 chamber being a new, 

 undetached bud. 

 Some buds become 

 quite separate and 

 grow into new individuals. In a few cases each 

 bud becomes detached, so that the animals always 

 remain of one chamber. 



Shell-forming Rhizopods are occasionally aggre- 

 gated in great masses and sometimes at great depths 

 in the ocean. Such seems to have been their habit in 

 past times, and many of the chalky limestones consist 

 of the accumulated shells of extinct Foraminifera. 



Monera. Some related forms are even simpler 

 than these Rhizopods, as they not only want the power 

 of house-building but have no nuclei, and are thus the 

 simplest conceivable living beings, mere specks of 

 living jelly (fig. 9). Of these naked forms, some authors 

 make a separate class under the name Monera. 



Two forms of Protozoa. Protamceba pri- 

 tuitiva, the simplest living animal: Mago- 

 sphcera planula, a compound form. 



