BIOLOGICAL INTRODUCTION. 



The lowest forms of flagellata are the trypanosomata, a parasitic 

 type of which is shown in Fig. 2. These forms have lately be- 

 come of medical interest because of their apparent causal relation 

 to certain tropical diseases. 



Common examples of the ciliated protozoa that are found in 



FIG. 2. Frog's Blood. A, Trypanosome ; B, eosinophile. (Williams.) 



ponds and stagnant pools are Paramecium and .Vorticella (see 

 Figs. 3 and 4). 



The former is a free swimming form, rather oval and somewhat 

 flattened in shape, with a mouth-like aperture at one side, leading 

 into a short stomach-like pouch. The animal is covered with cilia 

 which are longer in the mouth region and at the posterior end. 

 A nucleus can be distinguished, as well as two contracting vesicles, 

 one at either end of the animal. 



The Vorticellae are seen as solitary individuals, consisting of an 

 oval body mounted on a long stalk which is attached to some for- 

 eign body. At the free end, a flattened disc surrounded by cilia is 

 seen. At one side of this is the aperture known as the mouth. 



On closer examination, it is seen that the band of cilia does not 



