32 PROTOZOA 



animal found active in infusions of decaying vegetation. It is 

 readily obtained from hay immersed in water (Fig. lo, A and E). 



The outer covering or ectosarc has at its outer edge a thin 

 cuticle which tends to keep the animal of the same shape although it 

 is able to bend laterally. An oral groove running obliquely from the 

 anterior end to about the middle of the body aids in producing a 

 spiral movement as the cilia beat. The cilia are found all over the 

 body in spiral lines, and are especially prominent along the oral 

 groove and along the anterior and posterior ends. Under the cuticle 

 the ectoplasm contains a layer of protective organs called tricho- 

 cysts. The trichocysts in Epistylis umbellaria, a peritrichous 

 ciliate, are found in minute capsules arranged in pairs, each con- 

 taining a coiled thread. They are similar to the nematocysts, which 

 are characteristic of Coelenterates. The endoplasm contains 

 vacuoles, nuclei and food balls of ingested bacteria which traverse 

 the endoplasm along a definite path. 



Locomotion. — The cilia beating violently in unison direct the 

 animal forward, or reverse it, and the spiral lines give the spiral 

 rotation which keeps the course of the animal in a straight line. 



Digestion. — The cilia lining the oral groove direct particles of 

 food towards the mouth, and an undulating membrane (formed by 

 fused cilia) forces them down the gullet and into the interior of the 

 animal. The same type o{ gastric vacuole characterizing the Ameba 

 is found in Paramecium, Microchemical determinations have 

 shown that dilute HCl is formed around the food particles and that 

 protein digestion takes place. Excretion of indigestible material 

 is through a definite excretory aperture, the anus. 



Circulation. — As in Ameba we find no circulatory canals. The 

 action of the two contractile vacuoles removes fluid. Water is 

 taken in by the mouth with the food which is distributed in the 

 movement called cyclosis. 



Respiration. — Oxygen is taken in, and CO2 is extruded, through 

 the whole surface of the animal. The contractile vacuoles aid in 

 gaseous interchange. 



Excretion. — Indigestible material not attacked by the HCl in the 

 food vacuoles is extruded at once along the oral groove by the 

 reversal of direction of the ciliary beat and the contractile vacuoles 

 are supposed to aid in excretion of liquids and possibly of nitrogenous 

 wastes, as well as gases. The anal aperture extrudes wastes subse- 

 quent to digestion. 



