THE BEHAVIOR OF INFUSORIA; PARAMECIUM 



43 





tending from the mouth in the middle of the body forward to the anterior 

 end. When the animal is placed with the oral surface below, the groove 

 extends from the right behind 

 toward the left in front (see Fig. 

 32). The animal is thus not bi- 

 laterally symmetrical, but slightly 

 spiral in form. The surface oppo- 

 site the oral groove is marked by 

 the presence near it of two large 

 contractile vacuoles ; this may be 

 called the aboral surface. By con- 

 sidering the oral surface as ventral 

 we may distinguish for convenience 

 right and left sides. The entire 

 body is covered with fine cilia, set 

 in oblique rows. Those at the pos- 

 terior end are a little longer than 

 the others. 



As to internal structure, we may 

 distinguish an outer firm layer 

 known as the ectosarc, enclosing 

 an inner fluid portion, the endo- 

 sarc. The ectosarc is covered by 

 a thin outer cuticle; below this it 

 is thickly set with rodlike sacs, 

 placed perpendicular to the surface 

 and known as trichocysts ; the con- 

 tents of these may be discharged as 

 fine threads. The endosarc con- 

 tains two nuclei, the large macronu- 



cleus and the minute mirrormrleim food vacuoles ; 8> S ullet '' w > mouth; 

 Cieus dna me mmuie micronUCieUS, maC ronucleus ; mi., micronucleus; o.g., oral 



together with numerous masses of groove; P., pellicle; tr., trichocyst layer. 

 f^^A w.^f „f +1-.^™ „~„l~„„J ;„ The arrows show the direction of movement 



food, most of them enclosed m Q f the food vacuoles, 

 vacuoles of water. The endosarc 



is in continual movement, rotating lengthwise of the body, in the 

 direction shown by the arrows in Fig. 32. Between endosarc and 

 ectosarc, but attached to the latter, are the two contractile vacuoles, 

 which at intervals collapse, emptying their contents to the outside. 

 From the mouth (m) a passageway the gullet (g), leads through the 

 ectosarc into the endosarc. 



Fig. 32. — Paramecium, viewed from the 

 oral surface. L, left side; R, right side. 

 an., anus; ec, ectosarc; en., endosarc; j.v., 



ma., 

 macronucleus; 



