70 



PROTOZOA 



into a great number of very small hexagonal areas. From the center of 

 each of these areas arises a cihum. Just below the pelhcle is the clear and 

 relatively firm ectoplasm, often called the cortex, which contains a great 

 many spindle-shaped cavities placed with their longer axes at right 

 angles to the surface. These cavities are filled with a semifluid substance 

 and are known as trichocysts. They open to the outside along the lines 

 which bound the hexagonal areas. The ciUa are described as having an 

 axial thread continuous with the cortex and a covering continuous with 



Ectoplasm and 

 trichocysts 



EndopJasm 



Moicronucleus 



Food vacuole 



Pellicle 



Cilia 



Contractile vacuole 



Oral groove 



\ 



\ — Micronucleus 



r 



g — Mouth 

 Gullet 



Contractile vacuole 



Fig. 22. — Paramecnnn caudatum Ehrenberg. X 400. 



the pellicle. The endoplasm contains food vacuoles, two contractile vacu- 

 oles, and numerous granular masses various in size, shape, and character. 

 The contractile vacuoles, one at each end of the body, he between 

 the ectoplasm and endoplasm and are made up of a central space sur- 

 rounded by a system of radiating canals, from 6 to 10 in number. These 

 radiating canals end blindly in the cytoplasm at the outer end and at the 

 inner end empty into the central space, which in turn opens to the outside. 

 After the central space becomes empty, the canals discharge their con- 

 tents into it and then again gradually fill while the central space is being 



