176 



REPRESENTATIVE SINGLE-CELLED ANIMALS 



tained in the laboratory during long periods, so long in fact that 

 it may be regarded as an animal that can be thoroughly 

 " domesticated." 



The size of Paramoecium caudatum varies greatly, because, like 

 all other species of plants and animals that have been exhaus- 



Prorodon 



Euplotes 



DIdlnium 



Stentor 



Stylonichia 



l: 



Trichomonas 





/ 



r\ 



Lacrymaria 



Spirostomum 



Podophrya 



Lionotus 



Fig. 94. — Common ciliated and other protozoa from fresh water. 

 (Drawn in part by Wiley Crawford.) 



tively studied, the species is really composed of many races 

 which breed true among themselves but may differ widely when 

 one race is compared with another (c/. Fig. 308, p. 559). The 

 bod}'' is spindle-shaped with the anterior end bluntly rounded and 

 the posterior end more pointed. The older microscopists called 

 paramoecium the " slipper animalcule " because its shape seemed 

 to them to resemble the outline of a slipper. At one side is a 

 depression, the oral or buccal groove, passing diagonally from the 

 anterior end to about the middle of the body and ending in a 

 tunnel-like cavity, the cytopharynx, or gullet. The outer end of 

 the gullet is the cyfostome, or cell mouth. The cilia that clothe 

 the body are of uniform length, save at the extreme posterior end 



