THE INTELLIGENCE OF EARTHWORMS 



: ROBERT M. YERKES 



From the Harvard Psychological Laboratory 



Five figures 



" But some degree of intelligence appears to be exhibited in 

 this work [the plugging of the mouths of their burrows with 

 various objects by earthworms], — a result which has surprised 

 me more than anything else in regard to worms." * Thus wrote 

 Charles Darwin as a result of his careful study of the habits of 

 earthworms. Certain of his observations and the conclusion to 

 which he felt himself forced have been discredited by the recent 

 work of Miss Hanel. 2 Darwin, doubtless, was overliberal in his 

 ascription of "mental qualities" to the worm, but Hanel cer- 

 tainly has proved herself extremely critical and parsimonious. 

 In spite of the honest efforts of these excellent observers, and of 

 many other biologists who have paid special attention to the 

 behavior of earthworms, it must be admitted that we to-day 

 know little concerning the possibilities of habit formation in 

 these organisms. 



The present investigation, taking its start from the work of 

 Darwin, as critically repeated by Hanel, was planned for the 

 purpose of (a) demonstrating the ability or inability of the 

 earthworm to acquire direction-habits; (b) exhibiting the char- 

 acteristics of such habits as might appear; (c) discovering ex- 

 ternal and internal factors important in connection with such 

 habits; (d) determining the degree, of permanency of habits; 

 and (e) discovering the relation to the "brain" of such habits 

 as appeared. 



This paper is an introductory and preliminary account of an 

 investigation which is still in progress. It is limited to a de- 

 scription of the general method employed and to a detailed 

 account of the behavior of a single worm, No. 2, (Allolobophora 

 joetida), which was under observation from October, 191 1, 



1 Darwin, Charles. Formation of Vegetable Mould Through the Action of Worms. 

 New York: D. Appleton and Company, 1898, p. 35. 



1 Hanel, Elise. Ein Beitrag zur " Psychologie " der Regenwurmer. Zeit. fur 

 allg. Physiol., 1904. Bd. 4, S. 244-58. 



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