CHAPTEE 11 



PROTOZOA 



Chaeacteeistics. — Unicellular, or if composed of more than 

 one cell, such elements not arranged in tissues. Food ingested 

 hy a special mouth or ty any part of the cell substance. 

 Reproduction never takes place hy ova and spermatozoa. Some 

 forms are colonial. 



Group A. Gymnomyxa. 



The Protozoa have been divided into two groups, the 

 Gymnomyxa, corresponding with the old group Ehizopoda ; 

 and the Corticata, which comprise the Infusoria and Gregarin- 

 idea. The former group includes all those forms which, like 

 Amoeba, have, during the dominant phase of their hfe-history, 

 no limiting membrane. Their protoplasm is consequently 

 exposed, at any rate at one portion of their surface, and tends 

 to run into processes or pseudopodia, which vary in appearance 

 in the different species. Food may generally be ingested at 

 any point of the naked protoplasm. 



Although the amoeboid condition is the one in which 

 these organisms most frequently occur, they may pass through 

 other phases, such as rounded spores enclosed in a membrane 

 {chlamydospore), naked spores with a lash-shaped pseudopodium 

 {flagellula), etc. Not infrequently two or more individuals 

 fuse together, and this fusion may be the precursor of repro- 

 duction. When the bodies of numerous amoebiform indi- 

 viduals run together to form a large mass of protoplasm, the 

 result is known as a Plasmodium. 



