42 



Comparative Animal Physiology 



is not significantly different once they are adapted in media of different tonici- 

 ties. Figure 18 gives the rate of fluid elimination as a function of external 

 concentration. In actively feeding specimens "the rate of elimination is in- 

 versely linearly proportional to the concentration of the culture fluid."^^'"' 



Vahlkampfia calkensi, an amoeba parasitic in the oyster digestive tract, was 

 kept growing and multiplying in sea water on agar. ^^"^ Under these condi- 

 tions it had no contractile vacuole. When it was transferred to a similar agar 

 culture made up with tap water or distilled water, one 'or more vacuoles devel- 

 oped and pulsated regularly. The more active the amoebae were, the more 

 frequent the pulsations. 



Several species of marine Peritricha survive in dilute sea water. In a dilute 

 medium the volume rises slightly; the vacuolar output initially rises, then 

 decreases to a new steady value higher than that occurring in 100 per cent 

 sea water (Fig. 19). It was possible to balance exactly the increased vacuolar 

 output by adding a nonelectrolyte of proper concentration. Kalmus ^-^ made 



TIME IN MINUTES 

 i?0 . IQO 



240 



^ I llOOXSW 



12 l^X SW 



120 ISO 



TIME IN MINUTES 



Fig. 19. Body volume in cubic micra (upper half of figure) and excretory output from 

 contractile vacuole (lower half of figure) in marine peritrich Cothtirnia successively in 

 normal sea water, in I2V2 per cent sea water, in 121/2 per cent sea water containing m/500 

 cyanide, in llVi per cent sea water, in I2V2 per cent sea water containing m/500 cyanide, 

 in 121/2 per cent sea water, and in normal sea water. From Kitching.^^^ 



similar observations on the marine ciliate Amphileptus gutta. After a week in 

 70 per cent sea water the vacuolar rate was 21 per cent higher than in normal 

 sea water; in 60 per cent sea water and lower concentrations, hypervacuohza- 

 tion was noticed. 



Numerous fresh-water Protozoa show eflfects the reverse of those shown by 

 marine Protozoa. The fresh-water Amoeba x^errucosa has been cultured in 

 10 per cent sea water.-"^" When the sea water concentration was increased 

 gradually the pulsation slowed and the contractile vacuole finally disappeared. 

 No vacuole was seen when the animals were in 50 per cent sea water. When 

 fresh water was added, the vacuole reappeared. 



Similarly fresh-water peritrichous ciliates showed considerable slowing of 



