PLATE 1 



EXPLANATION OF FIGURES 



The figures are reproduced at a magnification of 480 X with the exception of 

 figure 16 which is 1120 X. Figures 3, 4, 5, 6 and 8 were drawn from living ani- 

 mals slightly flattened under pressure. The others were outlined from fixed 

 preparations. 



In preparing these figures an attempt has been made to reproduce all the 

 various characteristics of the contractile vacuole observed. In general when 

 the vacuoles are expanded the radiating canals are not visible but in favorable 

 specimens or in animals under pressure they appear as thread-like rays as shown 

 in figures 2, 3, 4, 5 and 10. Note that in most cases the vacuoles lie in a line 

 parallel to the outline of the body. The anterior end of the paramoecium is 

 toward the upper part of the page in all the plates. In all the figures the con- 

 tractile vacuoles are not stippled. 



1 Paramoecium with three contractile vacuoles arranged in the most common 

 manner. 



2 Paramoecium with two vacuoles. 



3 Paramoecium with extra vacuole in the anterior end — a rare grouping. 



4 Paramoecium with four vacuoles in the usual position but with one vacuole 

 slightly displaced to the right. 



5 Paramoecium with four vacuoles in common arrangement. 



G Paramoecium with four vacuoles in the unusual grouping of two in the 

 anterior end and two in the posterior end. Note the slightly darker area across 

 the middle of the animal. 



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