294 EGBERT T. HANCE 



interesting to note that the anterior vacuole becomes from, three 

 to four times the diameter of those in the posterior end. This, 

 in the cases studied, was not true for the common two-vacuoled 

 race, neither vacuole, exceeding the other in size. 



IV. OBSERVATIONS ON THE BEHAVIOR OF THE VACUOLES 



To sum up briefly our knowledge of contractile vacuoles: 

 The contractile vacuole is a pulsating organ surrounded by 

 a membrane of physiological importance, belonging to the ecto- 

 plasm. These vacuoles form an osmotic system and the evi- 

 dence at hand shows them to function in part as excretory and 

 respiratory organs. 



a. Percentage of variation in contractile vacuole number 



After the pure lines that had been started had multiphed con- 

 siderably examination was made of a number of individuals in 

 each line. Apparently these high numbers of vacuoles were not 

 in every case passed on to the offspring for in all of the cultures, 

 whether started with three or four vacuoled paramoecia, there 

 were considerable numbers of two vacuoled forms. But on the 

 contrary in the pure lines started with three vacuoled forms there 

 were found individuals possessing four contractile organs. Ob- 

 servations made on one culture in the early days of the work 

 showed a range of variation in vacuole number in the following 

 percentages. 



per cent 



Two vacuoles 8.6 



Three vacuoles 65 . 7 



Four vacuoles 25 . 7 



Later and more accurate observations were made for a period 

 of thirty days on one culture (covering 663 individuals) and the 

 results for that time averaged showed the proportion to be: 



per cent 



Two vacuoles .* 16. 13 



Three vacuoles 66 . 48 



Four vacuoles 16 . 43 



Five vacuoles . 904 



