1038 EVOLUTIONAL MODIFICATIONS 



peculiar to ph\ K-ticall\ more ]:>riiniti\ c animals, sucli as birds, reptiles 

 and fish, which, l)eeause of its \erv ]:)rimiti\ eness, is known as palenkiyiesis. 

 These two types of motor organization, the new and the old, diller from each 

 other in certain decisive characteristics, j-'erhaps the one most essential 

 difTerence between them appears in the insertion of an appreciable ]3eriod of 

 latency between the receipt of the allerent stimuli and the production 

 of the corresponding motor response. This ])eriod of latency has resulted 

 in retarding the immediacy of rellex action. In that mter\al thus created 

 between the receipt of the allerent stimulus and the dispatch ot the 

 efferent im])ulse, pro\"ision is made for more ellective sensory associations, 

 more comjjlcx combinations of neural impulses acti\"ated by the approach 

 of the afferent stimulus. It also provides for such important conditioning 

 qualities of jnolor response as rellection, selection and the introduction of the 

 influences of previous experience as well as the acKantages of higher intelli- 

 gence. Such a period of latency has in it all of the possibilities of withholding 

 action for relati^•ely long intervals of time, and thus conferring the far-reach- 

 ing benefits of that important neural attribute known as inhihition. The real 

 advances of beha\ lor for which this new clement of motor organization 

 lays the foundation become obvious at once. For the direct reflex reaction, 

 it substitutes the deliberately considered act. For the limitt'd rellex motor 

 pattern, it substitutes the more comple\l\ orgamzt'd motor design. In 

 general, primltixe paleokinetic acti\it\ is in its nature much mort- mimedi- 

 ately rellex and has but little rellectixe character. It makes the most achanta- 

 geous use of automatic and routine precisions in motion, but, on the other 

 hand, permits of little or no \ariation in its reaction ])atterns. Neither does 

 it allow of much reconditioning by new mlhuiux's and elements. It is exqui- 

 sitely objecti\c in its execution which appears to be as rigidly jjrescribed as 

 it is invariable in production. It possesses all of the characteristics necessary 

 for generic ada|)tation and but lew of those t|ualities essential lor mcliA idual- 



