MORPHOLOGY 



85 



which Nassonov (1924) interpreted as homologous with the Golgi 

 apparatus of the metazoan cell. The injection canal extends up to 

 the pore. The ampulla becomes distended first with fluid transported 

 discontinuously down the canal and the fluid next moves into the 

 injection canal. The fluid now is expelled into the cytoplasm just 

 beneath the pore as a vesicle, the membrane of which is derived 

 from that which closed the end of the injection canal. These fluid 



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Fig. 28. Diagrams showing the successive stages in the formation of 

 the contractile vacuole in Paramecium multimicronucleatum (King) ; up- 

 per figures are side views; lower figures front views; solid lines indicate 

 permanent structures; dotted lines temporary structures, a, full diastole; 

 b-d, stages of systole; e, content of ampulla passing into injection canal; 

 f, formation of vesicles from injection canals; g, fusion of vesicles to form 

 contractile vacuole; h, full diastole. 



vesicles coalesce presently to form the contractile vacuole in full 

 diastole and the fluid is discharged to exterior through the pore, 

 which becomes closed by the remains of the membrane of the dis- 

 charged vacuole. 



In Haptophrya michiganensis, MacLennan (1944) observed that 

 accessory vacuoles appear in the wall of the contractile canal which 

 extends along the dorsal side from the sucker to the posterior end, 

 as the canal contracts (Fig. 30) . The canal wall expands and enlarg- 

 ing accessory vacuoles fuse with one another, followed by a full ex- 

 pansion of the canal. Through several excretory pores with short 

 ducts the content of the contractile canal is excreted to the exterior. 

 The function of the contractile vacuole is considered in the following 



