574 



BIOLOGY OF THE PROTOZOA 



In general all results that are based upon physiological differ- 

 ences must be cautiously interpreted. Thus with Uroleptus mobilis 

 individuals from the progeny of single ex-conjugants may be se- 

 lected at appropriate periods to show marked differences in divi- 

 sion-rates. One such individual may reproduce at the rate of 



Fiii. 235. — Variations in the 

 caudatuni. 



progeny of a single ex-conjugant of Paramecium 

 (After Calkins and Gregory.) 



17 divisions in ten days; another indi^'idual from the same line will 

 reijroduce at the rate of 8 divisions in ten days, and a third may 

 divide at the rate of only 2 diA'isions. One might erroneously 

 argue that these individuals represent the sifting out of an heredi- 



