No. 3-] BIOLOGY OF THE STENTORS. 547 



it be half the breadth of the animal. While the integument 

 has been opening, the contractile power of the endoplasm has 

 been gently forcing the mass outward. (Fig. 63, fc}) The 

 process often requires several minutes. As soon as the entire 

 mass has passed beyond the periphery of the animal's body, the 

 lips of the opening approach slowly, and completely cover the 

 exposed place.^ 



E. Contractile Vacuole. 



I have made several observations upon the rate of pulsation 

 of the contractile vacuole in 5. ccBndeus and 5. roeselii, and 

 find an unexpected amount of variation therein. This variation 

 cannot be accounted for by difference in temperature, for it 

 appears in consecutive pulsations of the same vacuole, when no 

 sensible change in temperature has intervened. 



The mode of discharge of the contents of the contractile 

 vacuole of 5. cceruleiis was clearly and accurately stated 

 by Moxon {'69); and the method in which the fluid is col- 

 lected, and the changes in form of the vacuole during 

 diastole have been elaborately described by Maupas ('83, p. 

 641). 



In regard to the intervals between the systoles of the 

 contractile vacuole, they have seemed to me to show variation 

 characteristic of individuals rather than a variation due to 

 change of temperature. The consecutive intervals, besides, are 

 very unequal. Thus, one individual of 5. roeselii observed by 

 me had a vacuole which contracted five times at intervals of 50 

 seconds, the air-temperature being 20° C. Another, at 17° C. 

 gave a record of four consecutive pulsations at intervals of 

 I min. 20 sec. Still another contractile vesicle pulsated four 

 times at unequal intervals: i min. 15 sec, 2 min., i min. 40 

 sec, 2 min. 10 sec, — showing thereby a difference of 55 

 seconds between the first diastole and the last. Unfortunately, 



1 Recent observations have led me to think that the mode of defecation is 

 influenced considerably by the nature of the excreta. When it is coarse and 

 matted together, the integument must open widely, as above described. But when 

 it is composed of minute, smooth, rounded bodies, a small opening is formed, and 

 the excreta forced through it in a stream. 



