16 



INTRODUCTION PROTOPLASM CELL 



FIG. 21. A LEUKOCYTE FROM HUMAN BLOOD IN 



ACTIVE AMEBOID MOTION. 



The figures indicate the successive forms assumed 

 by the cell. Drawings were made at intervals of one 

 minute. X 500. 



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(a) Ameboid n/o/ilih/ is exemplified in the movements of an ameba; 

 hence the name. This consists essentially in the formation of a proto- 

 plasmic process or pseudopodium, into which the main mass of proto- 



plasm flows, thus pro- 

 ducing progression (Fig. 

 20). The movement of 

 the white blood-corpus- 

 cles is of this sort (Fig. 

 21). 



(b) Ciliary motility 

 is characteristic of hair- 

 like processes of certain 

 cells; such processes or 



cilia represent essentially permanently differentiated delicate pseudo- 

 podia. The method of cilium formation is illustrated in its simplest 

 form in the transient vibratory processes that arise under certain condi- 

 tions on leukocytes (Fig. 225). In metazoa generally ciliated cells are 

 attached, motion being limited to the cilia, which are located 011 the free 

 border. The function of cilia is to pro- 

 pel secretions toward the surface. The 

 motion is wavelike and always in one 

 direction. The cilia are generally at- 

 tached to a double row of granules, the 

 'basal bodies' (Fig. 22), perhaps parti- 

 tion products of the centrosome. In 

 Protozoa, e.g., Paramecium (Fig. 3), 

 the entire surface of the cell may be 

 ciliated; the function of the cilia here 

 being progression, and the direction of 

 stroke is reversible. Certain cilia are 

 non-motile, e.g., in the epididymis, 

 where they are closely clumped into 

 brushlike masses (Fig. 25). The func- 

 tion of such cilia is, in part at least, to 

 furnish a means for the elimination of 



secretions. Flagellnte motion is to be regarded as a variety of ciliary 

 motion. A flagellum is commonly regarded as a more robust cilium. 

 The purpose of flagella is to propel the cells to which they are attached. 

 I'-iially in higher animals the number of flagella is limited to one to a 

 cell. The best examples of flagella are furnished by spermatozoa (Fig. 2.'! ) . 



FIG. 22. THREE CELLS FROM THE 

 EPIDIDYMIS OF THE RABBIT. 



The non-ciliated cell has a diplo- 

 some at its free border. The ad- 

 jacent ciliated cells have in place a 

 double row of 'basal granules' to 

 which the cilia are attached. (After 

 v. Lenhossek.) 



