556 WALDO SHUMWAY 



ber of contractile vacuoles. The first observation was made by 

 one of my students on an individual from, a mass culture de- 

 scended from my thyroid fed line. Since that time, September 

 25, 1915, I have been searching my thyroid and control lines for 

 individuals with peculiarities of the excretory system. I find 

 Paramaecia with three contractile vacuoles in my thyroid fed 

 lines with great regularity, usually between 20 and 30 per cent 

 of all the individuals observed being characterized by the extra 

 vacuole. In spite of the most painstaking observations I have 

 never found them either in the control line nor in the mass cul- 

 ture from which the C race was established, and I am satisfied 

 that there exists a definite causal relation between the appear- 

 ance of these abnormal Paramaecia and their thyroid diet. 



The small number of forms actually observed may be due to 

 a form of division in which two vacuoles go to one of the daughter 

 cells while the other will have but one, until the normal de novo 

 formation of the second vacuole. If then the extra vacuole is 

 not formed for a short time, both Paramaeca will appear to have 

 two contractile vacuoles, even though there be a predisposition in 

 one (or both) to form a third. Thus our observed number of tri- 

 vacuoled forms will be smaller than the expectation. 



Shortly after my attention had been turned to these remark- 

 able individuals, Hance's brief notice in Science ('15) appeared 

 describing similar phenomena in Paramaecia which had been 

 previously immunized to very high temperatures. Hance re- 

 ports the occurrence of Paramaecia with as many as six con- 

 tractile vacuoles but concludes ''The only definite statement 

 that may be made of this race is that it has a tendency to more 

 than two contractile vacuoles." He suggests that this poten- 

 tiality for extra vacuoles may have been acquired under the 

 stress of the unusual environment (a temperature of 40°C.). 



I have not found Paramaecia with more than three vacuoles. 

 The third lies midway between the other two organoids and pul- 

 sates in rhythm with the others. In all other characteristics 

 these trivacuoled forms appear perfectly normal. Figures 7 and 

 8 represent two of these Paramaecia from my thyroid fine after 

 more than a hundred generations of treatment. 



