76 PROTOZOOLOGY 



the contractile vacuole occurs near the posterior region of the peri- 

 stome and its content is discharged through a canal into the vesti- 

 bule, and in Ophrydium ectaium, the contractile vacuole empties 

 its content into the cytopharynx through a long duct (Mast). 



Of numerous observations concerning the operation of the con- 

 tractile vacuole, that of King (1935) on Paramecium multimicro- 

 nucleatum (Figs. 28, 29) may be quoted here. In this ciliate, there 

 are 2 to 7 contractile vacuoles which are located below the ecto- 

 plasm on the aboral side. There is a permanent pore above each 

 vacuole. Leading to the pore is a short tube-like invagination of the 

 pellicle, with inner end of which the temporary membrane of the 

 vacuole is in contact (Fig. 28, a). Each vacuole has 5-10 long col- 

 lecting canals with strongly osmiophilic walls (Fig. 29), and each 

 canal is made up of terminal portion, a proximal injection canal, 

 and an ampulla between them. Surrounding the distal portion, there 

 is osmiophilic cytoplasm which may be granulated or finely reticu- 

 lated, and which Nassonov interpreted as homologous to 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 a membrane which closed the end of the injection canal. These 

 fluid 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. The canal wall expands and enlarging acces- 

 sory vacuoles fuse with one another, followed by a full expansion of 

 the canal. Through several excretory f)ores with short ducts the con- 

 tent of the contractile canal is excreted to the exterior. The function 

 of the contractile vacuole is considered in the following chapter 

 (p. 103). 



Various other vacuoles or vesicles occur in different Protozoa. In 

 the ciliates belonging to Loxodidae, there are variable numbers of 

 MuUer's vesicles or bodies, arranged in 1-2 rows along the aboral sur- 

 face. These vesicles (Fig. 30, a-c) vary in diameter from 5 to 8.5/i 

 and contain a clear fluid in which one large spherule or several small 

 highly refractile spherules are suspended. In some, there is a fila- 



