180 Education through Nature 



contractile vacuoles, mouth, and oesophagus, are permanent, 

 as is also its shape and form. These facts that it has 

 polarity and several permanent organs show that the 

 Paramecium is a definite organization. 



3. PHYSIOLOGY, a. Movement, reflex action, and spon- 

 taneity. The Paramecium swims about continually in 

 the water by means of its cilia. It uses these as a boy 

 uses his arms in swimming. First, they are struck back- 

 ward forcibly and quickly and then they are brought for- 

 ward more slowly. It always moves with the blunt end, 

 the anterior, foremost. The anterior half of the body is 

 slightly twisted in connection with the groove leading 

 into the mouth, and in consequence of this twist the animal 

 spins round and round on its axis as it swims through 

 the water. It swims in a tolerably straight course with uni- 

 form velocity. After going for some distance in one direc- 

 tion it stops, turns, seems to hesitate for a moment, and 

 then darts off in a new direction. The Paramecium is 

 flexible and elastic, and in passing round an obstacle it 

 bends its body and seems to squeeze itself through an 

 aperture smaller than its own diameter. When it pushes 

 its body into a narrow space between the particles of sedi- 

 ment in the water, the more fluid endoplasm is pushed 

 back by the obstruction and accumulates at the posterior 

 end of the body, while the ectoplasm still follows the out- 

 line of the cuticle. After part of the body has been pushed 

 past the obstruction, the endoplasm, with the particles 

 it contains, flows rapidly through the narrow part into 

 the enlargement beyond. The Paramecium' s movement 

 is spontaneous and is not caused by any external influence. 



b. Nutrition. The Paramecium feeds only on organic 

 substances. It feeds chiefly on minute infusoria and 

 flagellata, which are swept into the mouth by the cilia lining, 

 the peristominal groove, and the entrance to the mouth 

 itself, and, as I have already said, the cilia in these regions 

 direct the currents toward the mouth and thus bring the 

 food. 



c. Digestion, respiration, and circulation. The diges- 

 tive organs can be most satisfactorily studied when the 

 animal has been fed with some colored substance, such as 

 indigo. You can then see (a) the currents which are caused 



