146 ZOOLOGY. 



3. There is usually what is known as a pulsating vacuole, 

 in which some of the more fluid cell-contents collects, to be 

 forced out of the vacuole again by the contraction of the denser 



protoplasm (Fig. 66, pv). 



FIG. 66. 



FIG. 66. Paramecium in optical section (semi-diagrammatic). A, anterior end; c, 

 cilia; e.c., ectosarc; e.n., endosarc; f.v., food "vacuole"; g, gullet; N, meganucleus; 

 n, micronucleus; o, oral groove, leading to the mouth; p.v., pulsating vacuoles in dif- 

 ferent stages of contraction; tr., trichocysts; v, food vacuole in process of formation. 



Questions on the figure. In what sense is the term " vacuole " descrip- 

 tive of the structures to which it is applied in Paramecium? Describe the 

 special adaptations of the anterior end. Judging from their distribution 

 have the cilia any other function than locomotion? In what way are the 

 food vacuoles formed? Why do some food vacuoles appear lighter than 

 others ? 



4. Reproduction is effected chiefly by dividing into two or 

 more parts or cells, which occasionally remain associated. The 

 nucleus, when present, divides with the division of the cell 

 (Fig. 6). 



189. Habitat. Protozoa in their active stages require 

 abundant moisture, hence they are found in water, fresh or 

 salt, and as parasites in the bodies of other animals. The 

 Sporozoa are parasitic. Some amoeboid Rhizopods infest the 

 digestive tract of man and other animals, producing irritation 

 and disease. The Infusoria occur in water in which there is 

 decaying organic matter and minute organisms of various 

 kinds. Volvox and Euglena, green forms often classed as 

 Protozoa, have the power which green plants possess of living 

 on the inorganic substances found in ordinary water. 



