CoGNiTic State of Energy 125 



tions of Jennings {^4^: 44, 47, 62, 85) supply an apparently 

 helpful answer in the case of the infusor Paramoecium, for in 

 causing the typical constant movement he says: *'The stroke 

 of the cilia is always somewhat oblique, so that in addition 

 to its forward or backward movement Paramoecium rotates 

 on its long axis. . . . The swerving in any given direction 

 is compensated by an equal swerving in the opposite direction; 

 the resultant is a spiral path having a straight axis." Again 

 he says: "Since in its spiral course the organism is successively 

 pointed in many different directions, the samples of water it 

 receives likemse come successively from many directions. 

 Thus the animal is given opportunity to 'try* the various differ- 

 ent conditions supplied by the neighboring en\aronment. Para- 

 moecium does not passively wait for the environment to act 

 upon it, as Amoeba may be said, in comparison, to do. On the 

 contrary, it actively intervenes, determining for itself what 

 portion of the environment shall act upon it, and in what part 

 of its body it shall be primarily affected by the varying con- 

 ditions of the surrounding water. By thus receiving samples 

 of the environment for a certain distance in advance, it is 

 enabled to react with reference to any new condition which it 

 is approaching, before it has actually entered these conditions." 



Further, in the highly interesting reactions to electric stimuli, 

 according to the strength and direction of the current, the 

 organisms show an extended or restricted rotation. The same 

 author also says: "Practically all the infusoria agree mth 

 Paramoecium in s"v\amming in a spiral when passing freely 

 through the water, and in the fact that when stimulated they 

 turn toward a certain side defined by the structure of the organ- 

 ism." ChilomonaSy Euglena, Colpidium, and other unicellular 

 types there described likewise show rotatory movement, not 

 under one but varied forms of stimulation. 



The group of the Rotifera is, according to the writer's 

 estimate, one of prime importance as forming the metazoan 

 starting point for most invertebrate groups (chap. 18). Since 

 the time of Ehrenberg, various careful observers have described 

 the rotatory movements shown, and these may be shortly 



