INFUSORIA. 159 



will be seen to contract and finally disappear, be- 

 coming again distended and vanishing at tolerably 

 regular intervals. These are the contractile vesicles 

 (figs. 27 a, 28 a, 37 a), and they contain a clear 

 liquid, the nature of which is uncertain. 



In many of the Infusoria is a round or elongate 

 granular body (figs. 31 a, 36 a), which is called the 

 nucleus, the term having been applied to it from a 

 notion that the Infusoria consisted of simple cells. 

 A minute red spot is also often seen at the anterior 

 end of the body, which is supposed to represent an 

 eye, and is called an eye-spot. The Infusoria are 

 propagated in several ways : by budding or gem- 

 mation, new beings sprouting out in a bud-like form, 

 usually from the base of the parent; by division, 

 either transverse (fig. 26 a) or longitudinal (fig. 34 b), 

 of the body gradually into two parts, each of which 

 subsequently becomes a perfect animal ; by encyst- 

 ing, the body contracting into a globular form, and 

 forming a firm coat around it, the contents becoming 

 resolved into a numerous progeny of young ; and by 

 conjugation and the agency of spermatozoa and ova. 

 We will now proceed to the examination of a few 

 species, arranging them in the order of the families 

 to which they belong. 



MONAD'INA. In this family the bodies of the In- 

 fusoria are very soft, and without a skin or integu- 

 ment ; they are also exceedingly minute, and will not 

 admit the particles of indigo. 



Mori as lens (PI. XI. fig. 16) is very minute, and 

 commonly found in old infusions. Its body is rounded 

 and flattened, and granular on the surface. At the 

 front end of the body is a whip-like or flagel'liform 

 (flagel'lum, a whip) filament, differing from a cilium 

 in being rigid at the base and moveable at the end 

 only, by which it is enabled to row itself through the 

 water with a wriggling motion. 



Cercom'onas glotiulus (fig. 17) has a spherical body, 



