MORPHOLOGY 77 



collecting canals with strongly osmiophile walls (Fig. 29), and 

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

 canal, and an ampulla between them. Surrounding the distal por- 

 tion, there is osmiophilic cytoplasm which may be granulated or 

 finely reticulated, 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 discharged vacuole. The function of the 

 contractile vacuole is considered in the following chapter (p. 98). 



Various other vacuoles or vesicles occur in different Protozoa. 

 In the ciliates belonging to Loxodidae, there are variable numbers 

 of Miiller's vesicles or bodies arranged in 1-2 rows along the 

 aboral surface. 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 filamentous connection between the spherules and the 

 wall of the vesicle. Penard maintains that these bodies are balanc- 

 ing cell-organs and called the vesicle, the statocyst, and the spher- 

 ules, the statoliths. 



Another vacuole, known as concrement vacuole, is a character- 

 istic organella in Butschliidae and Paraisotrichidae. As a rule, 

 there is a single vacuole present in an individual at the anterior 

 third of body. It is spherical to oval and its structure appears to 

 be highly complex. According to Dogiel, the vacuole is composed 

 of a pelhcular cap, a permanent vacuolar wall, concrement grains 

 and two fibrillar systems (Fig. 30, d). When the organism divides, 

 the anterior daughter individual retains it, and the posterior in- 

 dividual develops a new one from the pellicle into which concre- 

 ment grains enter after first appearing in the endoplasm. This 

 vacuole shows no external pore. Dogiel believes that its function is 

 sensory and has named the vacuole, the statocyst, and the en- 

 closed grains, the statoliths. 



Food vacuoles are conspicuously present in the holozoic Pro- 



