RHIZOPODA 



483 



CLASS III. : RHIZOPODA. 



In the film of the hay infusion in which we found the slipper animal- 

 cule we shall, after some little search, discover another organism 

 which resembles a minute speck of jelly. When at rest it soon begins 

 to push out blunt root-like processes (Ehizopoda = root-footed), by means 

 of which it slowly creeps about. When one of these " pseudopodia " 

 comes in contact with a food particle, the latter is surrounded by the 

 process and drawn into the body protoplasm. The indigestible remains 

 are expelled from some other part of the body, which latter is constantly 

 changing its shape. Hence, owing to the surface layer of the protoplasm 

 not being denser in these animals than the rest, we meet with quite different 

 arrangements to those of infusorians. Thus, the rhizopod requires 

 neither a mouth nor an anus ; it can protrude or retract now one part, 

 now another, of its soft, protoplasmic body, after the manner of a foot, 

 and accordingly possesses no constant 

 shape. For this reason it has been de- 

 scriptively named the Proteus Animalcule 

 (Amoeba). 



Others of these delicate organisms sur- 

 round their body with pretty shells com- 

 posed either of foreign bodies (sand granules) 

 or of chitinous or calcareous secretions. 

 The pseudopodia in such cases are extended 

 through one large opening or through 

 numerous minute pores, or foramina ; hence 

 such Protozoa are known as Forami- 

 nifera. 



Large strata of the earth's surface, e.g., 

 the chalk, are composed almost entirely of 

 the calcareous shells of these microscopic 

 creatures. They also cover immense tracts 

 of the ocean bottom, out of which in some 

 future age they may, perhaps, tower up as 

 high mountain chains. 



In another group of rhizopods, the pretty Radiolarians, only a 

 portion of the body protoplasm is surrounded by a shell or capsule, the 

 other portion lying outside of the latter. The skeletons of these minute 

 Protozoa, all of which are marine, display a marvellous variety of shape, 

 and, as may be seen from the illustration of Heliosphera actinota, a 



Amieba, with Protruded Pseu- 

 dopodia. ( x about 100 times.) 



K., Nucleus ; p.B., contractile 

 vacuole. The protoplasm con- 

 tains numerous ingested food 

 particles. Two of the pseudo- 

 podia are in the act of encom- 

 passing a diatom. 



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