246 



BIOLOGY OF THE PROTOZOA 



responses to common stimuli were operating and that a perfect 

 equilibrium was established throughout. 



Vitality, as the sum total of all the protoplasmic activities set 

 up in response to internal and external stimuli, is variable. Varia- 

 tions due to external conditions may be readily seen in the effects of 

 heat and cold. Increased temperature increases oxidation leading 



C 





Fig. 128. — Uroleptus mobilis. Division of double individual; type with two divi- 

 sion nuclei. A, stages in the fusion of the two sets of macronuclei independently; 

 B, two division nuclei and two new peristomes; C, division of the cell, each half with 

 two sets of nuclei. (After Calkins.) 



to more rapid movements including food-taking activities, more 

 active digestion, assimilation, growth and reproduction. It involves 

 more waste and more active pulsation of the contractile vacuole. 

 Conversely, decreased temperature slows up the entire series of 

 activities and vitality is reduced. In like manner any condition 

 of the environment which tends to quicken, to weaken, or to nullify 



