io6 BEHAVIOR OF THE LOWER ORGANISMS 



it for a while. Other Parameeia may gather in the same way, but after 

 a considerable time they one by one leave the dead leaf. Our Para- 

 mecium swims about again, being directed hither and thither by the 

 various changes in the chemical constitution or temperature of the water, 

 till it comes to a region containing more carbon dioxide in solution than 

 usual. It gives no sign of perceiving this, save perhaps by swimming 

 a Uttle less energetically than before. The area containing carbon 

 dioxide is small, and soon the animal comes to its outer boundary, 

 where the water drawn to its oral groove contains no carbon dioxide. 

 It stops, and tries different regions, by swinging its anterior end around 

 in a circle, till it again finds a direction from which it receives carbonic 

 acid ; in that direction it swims forward. Since it behaves in the same 

 way whenever it comes to the outer boundary of the carbonic acid, it 

 remains swimming back and forth within this region, and thus in time 

 explores it very thoroughly. Finally it comes upon the source of the 

 carbon dioxide, — a large mass of bacteria, embedded in zoogloea, that 

 are giving off this substance. The infusorian places itself against the 

 mass of zoogloea, suspends the activity of the body cilia, and brings a 

 strong current of water along the oral groove to the mouth. This current 

 removes some of the bacteria from the zoogloea and carries them to the 

 mouth, where they are swallowed. While the animal is thus occupied, 

 other Parameeia in their headlong course may strike against it. But 

 now it does not react to such a shock at all ; it remains in place, engaged 

 with its food taking. After the animal has been in this position for some 

 time, the sun begins to shine strongly on this part of the pool, heating 

 the water. All the free-swimming Parameeia in this region thereupon 

 begin to swim rapidly about, repeatedly backing and trying new direc- 

 tions, till a direction is found that leads to a cooler region. But our 

 Paramecium, busy with its food-getting, does not react to the heat at 

 all. The water becomes hotter and hotter, and after a time our infuso- 

 rian moves about a httle, turning over or shifting its position, but still 

 remaining against the zoogloea. All the free swimming specimens have 

 left this region long ago. As the water becomes still hotter, our Para- 

 mecium suddenly -leaves the mass of zoogloea and now dashes about 

 frantically under the influence of the great heat. It first swims back- 

 ward, then forward, and tries one direction after another. Fortunately 

 one of these directions soon lead it toward a cooler region. In this 

 direction it continues and its behavior becomes more composed. It 

 now swims about quietly, as it did at first, till it finds another mass of 

 bacteria and resumes the process of obtaining food. 



In this way the daily hfe of the animal continues. It constantly 

 feels its way about, trying in a systematic way all sorts of conditions, 



