352 ROBERT M. YERKES 



of the tendency to attempt to retrace the course thru the stem 

 of the T; (f) the similar disappearance of the tendency to turn 

 back after progressing well toward the exit tube. These several 

 bits of evidence, combined with the still more obvious increase 

 in the number of correct or shortest trips, justify the conclusion 

 that the worm is capable of profiting by experience in a sim- 

 ple maze. 



6. The correct performance of a thoroly ingrained habitual 

 act, of the kind studied in this investigation, is not dependent 

 upon the "brain" (portions of the nervous system carried by 

 the five anterior segments), since the worm reacts appro- 

 priately within a few hours after its removal. 



7. As the brain regenerates, the worm exhibits increased 

 initiative, its behavior becomes less automatic, more variable. 



8. Within four weeks after the operation the regenerated 

 segments appear superficially complete and the worm natur- 

 ally burrows in a mixture of earth and manure. 



9. Two months after the removal of the "brain," during 

 the last four weeks of which period no training was given, the 

 habit had completely disappeared from worm No. 2, the sub- 

 ject to whose responses this paper is devoted, and in its place 

 there appeared a tendency to turn in the opposite direction to 

 that demanded in the training. 



10. Systematic training for two weeks resulted in the partial 

 re-acquisition of the original direction-habit. 



11. The various facts recorded in this investigation indicate 

 that the removal and the regeneration of the first five segments 

 resulted in the development of a worm strikingly different in 

 behavior from the original worm, No. 2. 



All of the statements of this paper are based upon the be- 

 havior of a single worm, and all of the conclusions are subject 

 to modification in the light of results which are being obtained 

 with other individuals. It has seemed to the writer desirable 

 to present this individual study while the facts are fresh in his 

 mind and the details of the behavior may be used to advantage. 



The writer desires to acknowledge his indebtedness to his 

 friend and colleague, Professor Herbert W. Rand, for valuable 

 advice and aid in the investigation. 



