THE PAEAMECIUM AND ITS ALLIES 



227 



the foregoing are the Sporozoa, 1 which are minute rod- 

 like organisms, occurring as parasites in the body of 

 various kinds of higher animals, especially in the food- 

 tract. They increase by transverse division of their rod- 

 like bodies ; but periodically they encyst, and divide into 

 numerous " spores," which, under favorable conditions, are 

 set free in great numbers. 



FIG. 210. Amoeba, the proteus animalcule. Greatly magnified, n, the 

 nucleus ; 10. v, water vacuoles ; c. v, contractile vacuoles; /. v, food vacuoles. 

 E. B. Wilson, " The Cell." 



Of all Protozoa, probably the simplest is Amoeba. 2 This 

 type varies greatly in size, from 0.02 mm. to about 0.3 mm. 

 It appears as a clear, highly refractive body of changing 

 outline. The body does not look homogeneous when 

 viewed with a high power, but contains various granules 

 derived from ingested food, vacuoles of water, and a trans- 

 parent, slightly more d^nse, spherical or ellipsoidal body, 



1 <T7r6/)05, spore ; {a>ov, animal, 

 alteration. 



