ORGANIC ADAPTATION 



345 



direction. It thus reaches the surface film. 

 To this it responds by the avoiding reac- 

 tion (Fig. 225), finding a new position and 

 swimming along near the surface of the 

 water. . . . Swimming forward here, it ap- 

 proaches a region where the sun has been 

 shining strongly into the pool, heating the 

 water. The Paramecium receives some of 

 this heated water in the current passing 

 from the anterior end down the oral groove. 

 (Fig. 226.) Thereupon it pauses, swings its 

 anterior end about in a circle, and finding 

 that the water coming from one of the 

 directions thus tried is not heated, it pro- 

 ceeds forward in that direction. This course 

 leads it perhaps into the region of a fresh 

 plant stem which has lately been crushed 

 and has fallen into the water. The plant 

 juice, oozing out, alters markedly the chemi- 

 cal constitution of the water. The Parame- 

 cium soon receives some of this altered 

 water in its ciliary current. Again it pauses, 

 or if the chemical is strong, swims back- 

 ward a distance. Then it again swings the 

 anterior end around in a circle till it finds 

 a direction from which it receives no more 

 of this chemical ; in this direction it swims 

 forward. . . . 



" In this way the daily life of the animal 

 continues. It constantly feels its way about, 

 trying in a systematic way all sorts of con- 

 ditions, and retiring from those that are 

 harmful. Its behavior is in principle much 

 like that of a blind and deaf person, or one 

 that feels his way about in the dark. It is a 

 continual process of proving all things and 

 holding to that which is good." (Jennings.) 



The behavior of Paramecium leaves one 

 with the impression that the animal is 

 largely at the mercy of its surroundings — 





" 1* 



Fig. 226. — Diagram 

 to show the rotation on 

 the long axis, and the 

 spiral path of Parame- 

 cium. 1-4, successive 

 positions assumed. The 

 dotted areas with small 

 arrows represent the cur- 

 rents of water drawn 

 from in front. (From 

 Jennings.) 



