PHYLUM PROTOZOA 



41 



Reproduction involves binary fission, budding, and multiple 

 fission. In the Radiolaria the spores formed in the endoplasm 

 within the capsular membrane may be similar (isospores) or 



dissimilar in size (anisospores). 

 to be gametes, definite infor- 

 mation on this point is lacking. 

 Food consists largely of liv- 

 ing organisms captured by 

 lobose pseudopodia. 



Subclass Rhizopoda 



Though these spores appear 



The amoeba-like forms (Fig. 

 27), the Foraminifera (Fig. 26), 



A B T 



Fig. 26. — Shells of Foraminifera. A, 



Siphogenerina striatula; B, S. columnel- 



and the slime molds are the laris, seen in longitudinal section; C, 



most characteristic representa- Cydamina orbicularis, side view. {After 



^ Ciishman) . 



tives of this subclass. All 



forms of pseudopodia excepting the axopodia are found but 

 rarely combined in the same individual. A test is very com- 

 monly present. It may be of pseudochitin to which other 

 material such as silica are cemented or may consist of calcium 

 carbonate laid down between two chitinous membranes as in 



the Foraminifera. 



The genus Amoeba, so 

 commonly met in elementary 

 zoological laboratories has 

 many relatives that live a 

 parasitic existence in the 

 bodies of numerous inverte- 

 brate and vertebrate hosts. 

 The majority of these depen- 

 dent amoebae are either 

 harmless parasites or com- 

 mensals, though Endamoeba 

 histolytica (Fig. 27) and one or two other species cause dysen- 

 tery in man. 



Some shelled rhizopods such as Arcella, Euglypha, Centropyxis, 

 and Difflugia are apparently but amoebae that have acquired 

 houses and are hence included in the same order (Amoebida) . In 

 contrast, the Foraminifera (Fig. 26) have anastamosing pseudo- 

 podia and shells showing varying degrees of complexity. The 

 foraminiferan shells are of extremely diverse natures but usually 



Fig. 27. — Endamoeba histolytica in vegeta- 

 tive state. {Redrawn from Hegner) . 



