LOCOMOTOR AND PREHENSILE ORGANS 31 



ORGANS EMPLOYED IN LOCOMOTION AND CAPTURE OF FOOD. -The 



simplest organs which are used for purposes of locomotion are the 

 pseudopodia, characteristic of the Rhizopoda or amoebae (Fig. 5). They 

 are simply processes of cytoplasm which are formed from the surface of 

 the body. A small elevation of the ectoplasm occurs at any point, and 

 this gradually increases in size till the endoplasm also takes part in its 

 formation. When it has reached a certain size it may be withdrawn 

 gradually, and another formed in some other direction. On the other hand, 

 it may increase steadily in size till the whole body of the organism flows 

 into it. In this manner, by the regular production of pseudopodia, an 

 amceba may move from one spot to another. It is by means of pseudo- 

 podia passed around any object that food particles are ingested. The 

 movements and changes in shape associated with the formation and with- 

 drawal of pseudopodia are termed amoeboid movements, w^hich are exhibited 

 typically by the amoebae. Certain flagellates as well as Sporozoa, such as 

 the malarial parasites, may also move in this manner. The pseudopodia 

 may be blunt finger-like processes of a lobose type, or they may be relatively 

 long, thin, and tapering, and of a filose type. The long narrow filose 

 pseudopodia may remain separate from one another, or they may become 

 united by lateral anastomoses, so that an organism possessing many of 

 them appears to be surrounded by a fine network of cytoplasm, as in the 

 Foraminifera (Fig. 72). In the case of the Heliozoa and Radiolaria, the 

 filose pseudopodia are more permanent structures, known as axopodia, 

 and are supported by radially arranged axial rods secreted by the endo- 

 plasm, or formed as outgrowths from the central granule (Fig. 51). 



Flagella and cilia are more permanent organs of locomotion. The 

 former are characteristic of the Mastigophora, and the latter of the 

 Ciliophora. They are long, narrow, whip-like processes which are capable 

 of performing vindulating or lashing movements, which cause currents in 

 the medium and enable the organism to progress through it. A single 

 flagellum has essentially the same structure as a cilium, though it is usually 

 larger, and is capable of more violent lashing movements. Generally 

 speaking, the small number of flagella possessed by a flagellate fulfils 

 the functions of the large number of cilia possessed by a ciliate. A 

 flagellum, as pointed out by Alexeieff (191 le), consists of an axial filament, 

 for which the term axoneme, suggested to the writer by Colonel A. Alcock, 

 will be employed, and a thin sheath of cytoplasm (Fig. 157). The axoneme 

 itself takes origin in a minute granule, the blepharoplast, which is situated 

 in the cytoplasm, and sometimes upon the surface of the nuclear mem- 

 brane. The axoneme passes to the surface of the body, and there, acquiring 

 a thin sheath of cytoplasm, becomes the flagellum. There can thus be 

 distinguished an intracytoplasmic portion of the axoneme and a flagellar 



