6 THE CELL 



Paramecium aurelia and Paramecium caudatum (Fig. 50), there 

 is a system of conducting canals, which have been known for 

 a long time, and have been worked at more than any others ; 

 from each of the two dorsal vacuoles about eight to ten fairly 

 straight tubes radiate ; their course may be traced almost all over 

 the whole body. However, the two systems remain independent 

 throughout their whole extent." They are thickest in the neigh- 

 bourhood of the vacuoles, becoming gradually finer distally. 



The Paramecium affords us an excellent subject for a closer 

 study of the working of this peculiar apparatus. When both the 

 contractile vacuoles have attained their greatest size, their whole 

 contents are suddenly and energetically ejected to the exterior 

 through their efferent canals and pores, so that for a time the 

 vacuole cavities quite disappear. This condition, as with the 

 heart, is termed the systole, whilst the period during which the 

 vacuoles become a^ain filled with fluid, and hence distended and 

 visible, is called the diastole. 



They become filled in the following manner : Even before the 

 systole has commenced, the above-described conducting canals 

 have collected fluid from the endoplasm of the body of the infuso- 

 rian ; this fluid probably is charged with carbonic acid and other 

 decomposition products. According to Schwalbe (III. 21) the 

 process occurs in consequence of " the condition of pressure of the 

 fluid in the animal's body, this pressure being due to the ever-in- 

 creasing amount of water which is continually being taken in by 

 the mouth." The conducting canals can be easily seen, at this 

 time being full of water. They become swollen in the neighbour- 

 hood of the contractile vacuole, which is now fully distended, so 

 that they look like a circle of rosette-shaped vacuoles surrounding 

 it ; these have been called formative vacuoles by Biitschli. In 

 consequence of their being in this condition, the contractile vacuole 

 cannot, during its systole, discharge its contents back through 

 them, but only forwards to the exterior. As soon as the diastole 

 again occurs, the distended formative vacuoles empty themselves 

 into the contractile vacuole, which in consequence becomes visible 

 again ; it then gradually distends itself until it reaches its maxi- 

 mum size. Hence at the commencement of the diastole the emp- 

 tied formative vacuoles disappear for a time ; however, they con- 

 tinue to collect fluid from the parenchyma of the body until the 

 commencement of the next systole. 



When several vacuoles are present they generally empty them- 



