PROTOZOA 



l6l 



the Protozda was really understood. Many of them can endure 

 drying, and then take up active life again on the return of water, 

 so that thereupon, in a few hours, Infusoria may literally swarm 

 where none seemed to be. This is responsible for the long life 



Fig. 74. — A compound Foraminiferan — Nodosaria. a, aperture of shell; /, food particles 

 captured by the strands of protoplasm outside the shell; n, nucleus; sh, shell. 1-4, the successive 

 chambers of the shell; z, being the oldest. 



Questions on the figure. — Does this seem a colony or a single individual? 

 Why? Why is digestion possible outside the capsule? Compare this with figures 

 of Protozoa in which there is no large aperture to the shell. 



of the old belief that they arose by "spontaneous generation," 

 that is without parents. It is only in recent years that this 

 belief has been finally disproved. It is known that they do not 

 appear in water that has been boiled and kept free from ex- 

 posure to the air. Much brilliant work has been done on the 

 group in recent years, on structure, on behavior, and on their 

 relation to disease. 



201. Classification of Protozoa. — The following are the principal classes of 

 Protozoa 



Class I. Rhizopoda (root-footed). — Type: Ammba. The Rhizopoda are amoeboid 

 in form with pseudopodia, which may be either blunt (Fig. 67) or slender (Fig. 74). 

 The protoplasm may be naked {Amasba) or may secrete a shell either calcareous 

 {Foraminifera) or siliceous {Radiolaria). In the shelled forms the pseudopodia 

 pass out through openings in the skeleton (Fig. 75). Reproduction is usually by 

 division, or by the formation of many spores. Encystment frequently occurs. 



