INDIVIDUAL AND SOCIAL SURPLUS 555 



substance as carmine ink be introduced into the water so as to reach 

 Stentor's disk there are several reactions. At first the normal move- 

 ments of the cilia which cause a current of water to flow toward the 

 animal's mouth are not changed. The particles of carmine ink enter 

 the mouth and thence penetrate the internal protoplasm. If the cloud 

 becomes dense, however, the animal presently bends aside. If this 

 reaction is not effective in getting rid of the particles it is repeated. If 

 failure still results the ciliary movements are suddenly reversed to pro- 

 duce a current of water away from the mouth. This reversal is brief 

 but, if no improvement is effected, it may be repeated many times in 

 rapid succession. Next, contraction within the sheath may occur. By 

 this contraction the animal escapes stimulation entirely, but it also 

 obtains no food. Usually the animal extends itself again in less than a 

 minute. If particles of carmine are again met Stentor no longer reacts 

 in the milder ways employed at first, but contraction occurs at once. 

 This may be repeated many times, each period of retirement lasting 

 longer than the preceding one. Ultimately the animal contracts re- 

 peatedly and violently while still encased in its tube. It thus finally 

 detaches its foot from its moorings, leaves its tube, swims away, 

 attaches itself elsewhere and forms a new sheath in a new and more 

 favorable environment. 



This behavior differs from that of Paramecium in a radical way. 

 Paramecium, except when fatigue or other cause reduces surplus energy, 

 always reacts in the same way to the same stimulus. Stentor reacts 

 in different ways. As Jennings puts it " the change in reaction must 

 be due to a change in the organism " itself. In any event the present 

 readiness of this organism to react in one of two or more possible ways 

 depends on its past history. The animal profits by experience. The 

 change in reaction is regulatory, not haphazard. Something akin to 

 habit has appeared. This clearly marks the saving of much energy that 

 otherwise would be spent in useless attempts to avoid injurious condi- 

 tions. There is less waste and more surplus, more chance of survival 

 and a greater length of time during which the animal possesses a sur- 

 plus of energy over the minimum necessary for survival. 



To trace the gradual development of creatures more complex in 

 structure, and in consequence more complex in behavior, might be inter- 

 esting, but if the recent work of observers of animal behavior is to be 

 trusted no new principles are involved until the primates themselves 

 are approached. 



Throughout the period marked by this interval, however, countless 

 changes in the structure, in the production of new reflexes, in the 

 modification of instinctive behavior by the formation of habits, per- 

 fected the adjustment of individuals to the physical environment and 

 their accommodation to their fellow creatures. Definite complex com- 



