VARIATION AND CORRELATION IN THE 
EARTHWORM =\ 
By RAYMOND PEARL and WILBUR N. FULLER. 
1. Introductory. 
The purpose of this papei* is to present the results of a study of the variation 
and correlation exhibited in certain specific characters of the common garden earth- 
worms. 
The earthworm which occurs most abundantly in the region about Ann Arbor 
and with which we have dealt in the present work, has usually been identified as 
Lumhricus liercideus, Sav. or L. agricola, Hoffm. The counting and measuring 
and a portion of the computing were done by W. N. Fuller in connection with certain 
class-work in the University. The values of the constants were twice independently 
computed, and the paper written by R. Pearl. 
There were two principal reasons which led to the undertaking of this work. 
In the first place we wished to determine if possible more exactly than had 
previously been done the typical condition of the form of earthworm commonly 
found in this portion of the United States. The earthworm is such a generally 
used type form, both for laboratory teaching and for investigation in a number of 
fields, notably regeneration, that an exact determination of the existing type and 
variation with reference to the several specific characters seemed decidedly 
desirable. Secondly, the writer hoped to get from this form some light on certain 
general biometrical problems on which he is collecting data. 
The material for the work consisted of sexually adult specimens only. The 
criterion used to determine whether an earthworm was sexually adult, was the 
presence of a fully developed clitellum. That this is a justifiable criterion has 
been shown by Colef. 
* Contributions from the Zoological Laboratory, University of Micliigan, No. 89. 
+ Zool. Anz. Bd. xvi. pp. 440 and 453. 
