CHAPTER II. 



THE MONAD AND OTHER INFUSORIANS. 



IF we allow a little dried grass or hay or a piece of fish or 

 flesh to stand in a glass of water for a day or two, thus 

 making what is called an infusion, and then examine a drop 

 of this water, it will be found to teem with myriads of 

 microscopic creatures, called 

 Infusorians, because they are 

 found in infusions. The sim- 

 plest and minutest form of in- 

 fusorian is the monad (Fig. 11). 



In swimming, the monad 

 stretches out the whip-lash-like 

 appendage called the flagellum, 

 which vibrates with an undulat- 

 ing, whirling motion, and pro- 



a peculiar graceful rolling FIG. 11 Monad from an infusion of 

 ,. ' ,, ,, , TT , decayed flesh. Heteromitaputrina 



motion OI the monad. When Stokes. (Magnified 1500 diameters) 



the monad is fixed, the flagellum is used to convey food to 

 the mouth, which lies between the base of the flagellum 

 and beak, or " lip." The food is thrown by a sudden jerk, 

 and with precision, directly against the mouth. 



Ascending a step higher, we come to Infusoria Avhich are 

 covered with cilia, or hair-like processes, by which they glide 

 about over submerged leaves, etc. One of the largest and com- 

 monest Infusorians is the Parmneciwm (Fig. 12). This 

 animalcule is a mass of protoplasm, representing a single 

 cell. In the body-mass are excavated a rude mouth, and a 

 throat leading to a so-called stomach or digestive cavity. 

 Three hollows in the body form the contractile vesicles. 



