RHIZOPODS. Ill 



their soft bodies a protective shell, often of exquisite 

 form and remarkable construction. Thus the mem- 

 bers of one genus, Difflilgia, build themselves shells of 

 sand grains cemented together with the most perfect 

 regularity, every grain exactly fitting to its place. 

 Yet, when the young Dififliigia happens to be where 

 suitable sand is scarce, it will build its shell of 

 diatoms,-"- often using those that are longer than the 

 completed covering, attaching them lengthwise, side 

 by side, and parallel to each other. Another genus, 

 Arcella, secretes from its body a brown shell of 

 delicate membrane which, with a high power, is seen 

 to be formed in minute hexagons. And still another, 

 Clathrulina, the most beautiful of all the fresh-water 

 Rhizopods, lifts itself on a long stem, and there 

 surrounds its body by a hollow latticed sphere, and 

 through the large and rounded openings in the walls 

 extends its pseudopodal rays in search of food. 



In the unprotected forms — those without a shell — 

 the pseudopodia are protruded from any part of the 

 body; in those furnished with a " shell they are pro- 

 truded from that portion of the body immediately in 

 contact with the mouth of the shell, through which 

 they often extend for a long distance as exceedingly 

 fine,' branching threads. With a few exceptions the 

 bodies of the Rhizopods are colorless; in those excep- 

 tions the coloration is usually due to the presence of 

 colored food, and so is diffused throughout the entire 

 protoplasm, or it is confined to the parts near the 

 surface, the central portion being nearly colorless. 

 The pseudopodia are always colorless. 



Not only do the Rhizopods move by means of these 

 "false feet," but they capture food with them, consum- 



