PROTOZOA. l6l 



distributing the parasites has changed our 'whole treatment of 

 sanitation as it relates to these diseases. 



177. Comparison of Protozoa: a Practical Exercise. Let the 

 student examine samples of all the stagnant waters in the laboratory. 

 Look along the sides of the vessels, in the ooze at the bottom, on the 

 sticks and algas. Find all the different kinds of Protozoa that you 

 can. Compare them with the descriptions and with figures, and 

 see which of the types they most resemble. In what respects do all 

 the kinds agree? In what particulars do they most differ? In 

 how many different ways do you find them moving? How do the 

 smallest and the largest compare in size? What have you seen 

 as to their foods? 



Study the figures and descriptions in the larger text-books, and 

 find to what extent the form and size of the nucleus differ in Protozoa. 

 In how many different ways do you find Protozoa reproducing? 

 What kinds of Protozoa form shells? What do they lose and what 

 gain by having the shells? 



178. Definition of the Protozoa. The Protozoa, then, are animals 

 made up of one cell or of several similar cells loosely joined together 

 (colony). The chief method of reproduction is by the division of 

 the animal into two. Each of these may grow to the original size 

 and divide again. In many cases two individuals may unite (con- 

 jugate), after a long series of divisions. This seems in some way to 

 renew the powers of the protoplasm in such a way that the divisions 

 may then take place more actively again. 



179. Classification of the Protozoa. 



Internal parasites; almost no organs of locomotion. . .Sporozoa. 



Examples: Plasmodium malaricg; Gregarina. 

 Free forms; protoplasmic appendages or processes. 



Appendages temporary (that is, retractile) Rhizopoda. 



No shell: Ameba (many species). (Fig. 35.) 

 With shells: Radiolaria; Foraminifera, etc. (Fig. 37.) 

 Appendages permanent. 



One or few and large (flagellum) Flagellata 



Examples: Euglena, Eudorina, Volvox. (Fig. 40.) 



Several or many, and small Infusoria. 



Cilia Ciliata. 



Examples: Paramecium; Vorticella; Stentor (Figs. 38 

 and 39). 



Sucking tentacles Suctoria. 



Example: Podophrya (Fig. 40). 



