The Protozoa 



149 



of minute particles of sand and other foreign objects held together by 

 chitin. 



Fig. 63. 



A. Amoeba proteus. (After Gruber.) 



B. and C. Arcella discoides. (After Leidy.) 

 D. Difflugia urceolata. (After Leidy.) 



11. Order 2. Heliozoa ( ) Rhizopoda with 



thin, radially arranged pseudopodia, which are usually supported by 

 axial threads. 



Examples: Actinophrys. (Fig. 64.) 



Actinophrys ( ), the sun animalcule, lives 



among the aquatic plants in fresh-water ponds 

 and ditches. The body appears vesicular, be- 

 cause it is crowded with vacuoles. The small 

 organisms which serve as food strike the 

 pseudopodia, pass down to the body, and are 

 engulfed ; larger organisms are drawn in by 

 several neighboring pseudopodia acting to- 

 gether. 



12. Order 3. Radiolaria ( ) 



Marine Rhizopoda with raylike pseudopodia, a 

 central perforated capsule of chitin, and usually 

 a larger enclosing skeleton of silica. 

 Examples: Actinomma, Thalassicola. (Fig. 65.) 

 The shells of the radiolarians, upon sinking to the sea bottom, form 

 radiolarian ooze. This becomes hardened, producing rock strata as much 

 as 1,000 feet thick. These rocks may take the form of quartzites, flint, 

 or chert concretions. 



13. Order 4. Foraminifera ( ) Rhizopoda, 



mostly marine, with fine, branching pseudopodia which fuse, forming a 

 protoplasmic network. 



Examples: Allogromia, Globigerina. (Fig. 66.) 

 Allogromia ( ) lives in fresh water and has a 



chitinous shell. The shells of many Foraminifera consist of numerous 



Fig. 64. 

 Actinophrys sol 

 (From Bronn.) 



