Chap. 21 



THE PROTOZOANS 



427 



RESULTS OF A LONG EVOLUTION 



Glassy frame 



Chambered shells 



Swims, gifdes, 

 by cilia 



Swfms by 

 loshing "neck" 



Eye with 

 lens 



B C 



Didinium eats o Paramecium 



6. 



Fig. 21.1. Protozoans are the results of an evolution that was under way long 

 before multicellular animals appeared. Here are a few examples of their special 

 structures. Protecting shells. 1, Clathrulina elegans extends its delicate pseudopodia 

 through the openings in its glassy basket. 2, three types of the multichambered 

 shells of foraminiferans that are secreted and occupied, one chamber after another 

 until in the last one the owner reaches full size. Locomotion. 3, Kerona polyporiini 

 glides by means of cilia over various species of hydra. 4, Lacrymaria olor swims 

 by lashing movements of its swanlike neck. Sensory organs. 5, Pouchetia has a 

 relatively enormous light receptor, a lens and cup containing the visual pigment 

 carotene similar to that in eyes of multicellular animals. Weapons of attack and 

 defense. 6, Didinium attacks and devours a paramecium which has thrown out its 

 poisonous trichocysts without effect. (Courtesy, Jahn and Jahn: The Protozoa. 

 Dubuque, Iowa, Wm. C. Brown and Co., 1949.) 



