PROTOZOA. 



241 



They possess no cilia. The representative forms are Amoe- 

 bae, Foraminifera, 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- 

 esses, and eats by wrapping 

 its body around the particle of food 

 from T V to woo- 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 Amoeba 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 



Fig. 185. — Amoeba princeps, X 150; the 

 same animal in various shapes. 



The size ranges 



Fig. 186.— Rhizopods: a, a monothalamous, or single-chambered, Foraminifer (La- 

 gena striata) ; 6, a polythalamous, or many-chambered, Foraminifer (Polystomella 

 crispa), with pseudopodia extended; c, a Radiolarian, one of the Polycystines 

 (Podocyrtis Schomburgkii). 



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