MORPHOLOGY 



45 



cised in using them for taxonomic consideration of the Protozoa. 

 Flagella. The flagellum is a filamentous extension of the cyto- 

 plasm and is ordinarily extremely fine and highly vibratile, so 

 that it is difficult to recognize it in life under the microscope with a 

 moderate magnification. It is most clearly observed over a darkfield 

 condenser. Lugol's solution (p. 721) stains it, though the organ- 

 ism is killed. In a number of species, the flagellum, however, can be 

 seen in life as a long filament, as for example in Peranema. As a rule, 

 the number of flagella present in a single individual is small, varying 

 from one to eight, but in Hypermastigina there are numerous fla- 



5^®ID 



Fig 

 forms 

 dition of KOH solution to the water 



7. Form-change in a limax-amoeba (Verworn). a, b, contracted 

 c, individual showing typical form; d-f, radiosa-forms, after ad- 



gella. A flagellum appears to be composed of at least two parts (Fig. 

 8, a, b). An elastic axial filament takes its origin in the basal granule. 

 Surrounding this filament there is a sheath of contractile cytoplasm 

 which varies in thickness alternately on the opposite sides of the 

 filament. The flagellum ordinarily tapers toward its distal end where 

 the axial filament is said to be frequently exposed. 



Vlk (1938) found, besides the kind mentioned above which he 

 called the whip-flagellum, another form named by him ciliary flagel- 

 lum. The latter is said to be uniformly thick, but possesses dense 

 ciliary projections which are arranged on it in one or two spiral rows 



