154 



Fig. 68. Paramecium in optical section (semi-diagrammatic). A, anterior end; c, cilia; e.c. 

 ectosarc; «.n., endosarc; /.v., food ''vacuole"; g. gullet; N, meganucleus; n, micronucleus; o, oral 

 groove, leading to the mouth; p.p.. pulsating vacuoles in different stages of contraction; tr., tricho- 

 cysts; ff, food vacuole in process of formation. 



Questions on the figure. — In what sense is the term "vacuole" descriptive of 

 the structures to which it is applied in Paramecium? Describe the special adapta- 

 tions 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? 



194. Habitat. — Protozoa in their active stages require 

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

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

 Sporozoa are parasitic. Some amoeboid Rhizopoda infest the 

 digestive tract of man and other animals, producing irritation 

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

 decaying organic matter and minute organisms of various 

 kinds. Vohox and Euglena, green forms often classed as 

 Protozoa, have the power which green plants possess {photosyn- 

 thesis) of building up carbohydrates from CO2 apd water in the 

 presence of sunlight. 



195. Organization. — We cannot say that Protozoa have 

 organs in the sense in which we have defined that term hitherto, 

 yet they are certainly organized. The organization shows 

 itself in the nucleus, in the distinction of ectosarc and endosarc, 

 in the pulsating and food vacuoles, in temporary projections 

 of protoplasm called pseudopodia, in more permanent vibratile 

 projections of the ectosarc known as cilia or flagella, in the 

 mouth — found in many forms, in cell-wall and secreted skele- 



