78 



THE CELL 



place to place much more rapidly than can be effected by means 

 of pseudopodia. Flagella and cilia are delicate hair-like processes, 

 which extend in greater or less numbers from the surface of the 

 cell. They are composed of a homogeneous, non-granular sub- 

 stance, and in this respect resemble short, thin pseudopodia, 

 when these consist of hyaloplasm alone. However, they differ 

 from pseudopodia in two respects : firstly, they move in a different 

 and more energetic fashion, and secondly, they are not transitory, 

 but permanent organs, being neither protruded nor withdrawn. 

 Fundamentally, however, the movements of flagella and pseudo- 

 podia are identical in kind, as is shown by the observations made 

 by de Bary (I. 2) on swarmspores of Myxomycetes, and by 

 Haeckel, Engelmann, R. Hertwig (III. 12b), and others on 

 Rhizopoda. 



Many of the lower organisms reproduce themselves by means 

 of small spores, which resemble Amoebce in their appearance and 

 in their mode of movement (Fig. 43). After a time such spores 

 usually protrude two thread-like pseudopodia (Fig. 43 a), which 

 exhibit slow oscillatory movements, and develop into flagella, 



whilst the remainder of the 

 body withdraws all its other 

 pseudopodia, and so becomes 

 spherical in shape. As the 

 movements become stronger, 

 the spore travels more and 

 more rapidly, by means of its 

 two flagella, through the water 

 (Fig. 43 b) ; thus a " swarm- 

 spore " has developed out of the 

 little amoeboid cell. 



It may be safely deduced from 

 these discoveries that flagella 



a 



B 



Fig. 4-3. Microsomia socialis. An amoe- 

 boid cell (a) which has been produced by 

 division, and has wandered from the 

 colony ; and which, having withdrawn all 

 its pseudopodia, with the exception of two, 

 which have developed into flagella, be- 

 comes transformed into a swarmspore (b). 

 (From Hertwig, PI. 6, d and e.) 



are developed from delicate protoplasmic processes, which become 

 especially contractile, and in consequence differ somewhat in their 

 properties from the remaining protoplasm. Hence they may be 

 considered as constituting a special plasmic product or cell-organ, 

 composed of contractile substance. 



Flagella and cilia always arise directly from the body of the 

 cell. If the cell is enveloped by a membrane, they protrude 

 through pores in it. At their bases they are always somewhat 

 thickened, frequently starting from the surface of the protoplasm 



