5^*1 Hardy, Note on the Contractile Vacuole. 47 



NOTE ON THE CONTRACTILE VACUOLE. 

 By A. D. Hardy, F.L.S., F.R.M.S. 



{Read before the Field Naturalists' Club of Victoria, 12th April, 1914.) 



While engaged on the examination of some sphagnum from 

 Mount Baw Baw {Victorian Naturalist, March, IQ14), my 

 attention was arrested by a protozoon which, though not at 

 first, at a later stage seemed like a form of Amoeba, possibly 

 a young A . proteus ; but, as I am not well informed as to the 

 behaviour of vagrant Rhizopods escaped from tests, such as 

 Diffiugia and Arcella, and, as will be seen, this organism 

 differed in many respects from Amoeba, the identity must 

 remain unsolved. 



When first seen the animal was slowly moving in a straight 

 line across the field of view, without any alteration of shape, 

 this syrrlmetrical form being kept continuously throughout the 

 greater part of the half-hour during which it was under 

 observation, progression being in a direction indicated by the 

 long axis of the cell with the obtusely rounded end foremost. 

 The most careful scrutiny revealed no sign of organs of loco- 

 motion, such as cilia or flagellum. Observation of the organism 

 as a whole and of its contractile vacuole absorbed my attention 

 to the exclusion of other interesting matters, such as the 

 nucleus, which, if present, was indistinct. During the steady 

 rectilinear progress of the cell, which appeared to move in a 

 slug-like manner, there was a rhythmic production of a vacuole 

 which regularly came first into view at a point near the 

 extremity of the attenuated posterior end. It moved forwards 

 in an axial line to near the anterior end and back again to the 

 posterior, where it disappeared. 



During half an hour there were six such formations, the 

 time occupied by each course being about five minutes. The 

 time covering diastole and systole, as recorded for other forms 

 by several observers, appears to be about 60 seconds. 



There was no systole in the usual acceptation of the term. 

 Instead, the vacuole enlarged from the time of its origin until 

 its sudden collapse, or escape, with almost explosive force at 

 the extremity of the cell. 



On reappearance, the pn >< m <■ oi the vacuole, now minute, 

 was betrayed by its movements. As it moved along the cell 

 its progress was ;it .1 rate distinctly less than that of the proto- 

 plasmic stream. It has been suggested by one writer that as 

 the vacuole fills il becomes heavier than the endoplasm sur- 

 rounding it and so lags behind, the observation being made 

 in connection with Amoeba. Constantly increasing, it paused 

 momentarily near the cells anterior, and then began its retro- 

 grade course, during which it apparently increased in size, 



