OF THE ALIMENTARY TRACT 7 



for feeding. Their protrusion seems to be by ex- 

 ternal stimulus on the part of desirable food sub- 

 stances. 



Thus there is a primitive sense system, corres- 

 ponding to the sight, smell, taste, and touch organs 

 of higher animals. 



A protozoon possessing pseudopodia is known as 

 an amoeba (change). 



Some protozoa have, instead of pseudopodia, 

 flagella (whip). A flagellum is a lash-like filament 

 extended as a more or less permanent organelle from 

 the surface of the body, the number and position of 

 these processes varying with the species of flagellates, 

 so named from this feature. 



A flagellum is constructed of a filamentous core 

 attached centrally to certain little bodies called 

 blepharoplasts which are intimately connected with 

 the nuclear apparatus, the central control organ, this 

 core projected through the surface membrane or 

 ectoplasm and carrying the covering with it. Fla- 

 gella are moved in rythmic lash-like manner and 

 serve as organs of locomotion and food gathering. 

 They evidently have tactile sense. In food gathering 

 they whip or brush particles into contact with the 

 surface of the body, w^here they are then ingested. 

 They are used as propellers in free swimming loco- 

 motion and protozoa possessing only this means of 

 propulsion usually move about in a jerky manner. 

 Smoother movement of some flagellates results from 

 other swimming appendages or from a posteriorly 



