PROTOZOA. 



241 



They possess no cilia. The representative forms are Amce- 

 bce, Forartiinifera, and Polycystina. 



An Amoeba is a naked fresh-water Rhizopod; an in- 

 definite bit of protoplasm, as structureless as a speck of 

 jelly, save that it is made of 

 two distinct layers, and has a 

 nucleus and a contractile cav- 

 ity inside. It thus differs 

 from the Monera. It has no 

 particular form, as it changes 

 continually. It moves by put- 

 ting forth short, blunt proc- Fl . A r,>ceba ep s, x 150 ; the 

 esses, and eats by wrapping Bame auimal iu various 8hai)e8 - 

 its body around the particle of food. The size ranges 

 from -fa to -sVoir of an inch in diameter. Specimens can 

 be obtained by scraping the mucous matter from the 

 stems and leaves in stagnant ponds, 



A Foraminifer differs from an Amoaba in having an 

 apparently simpler body, the protoplasm being without 

 layers or cavity ; its pseudopodia are long and thread-like, 

 and may unite where they touch each other. It has the 

 property of secreting an envelope, usually of carbonate of 



a 



FIG. 186. Rhizopods : a, a monothalamou*, or ^ngle-chambered, Fornminifer (Lo- 

 gena striata) ; b, a polythalamous, or many-chambered, Foraminifer (Polystomella 

 criApa), with pseudopodia extended ; c, a Radiolarian, one of the Polycystiues 

 (Podocyrtis Schomburgkii). 



16 



