200 



MICHIGAN ACADEMY OF SCIENCE. 



VARIATION AND CORRELATION IN THE EARTHWORM. 



RAYMOND PEARL AND WILBUR N. FULLER. 



(Abstract.) 



A statistical study of variation in the common earthworm, Lumhricus 

 agricola Hoffm.. included the following characters : 

 I. The total number of somites in the body. 

 II. The total length of the body. 



III. The number of somites from the anterior end of the worm to 

 the clitellum. 



IV. The number of somites in the clitellum. 



The worms measured were all collected from a restricted area in the 

 city of Ann Arbor. The collection was entirely at random. Only those 

 individuals were measured which were sexually adult, and consequently 

 bore a clitellum. 



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EXPLANATION OP FIGURE. 



Fig. 1. Frequency polygon of variation in the number of somites in the body of the common 

 earthworm. Abscissae, number of somites; ordinates, number of individuals. S. D. = Standard 

 deviation. 



The poh'gon of frequency, showing the variation in the total number 

 of somites in the body, is shown in Fig. 1. The constants for this poly- 

 gon are given in the following table : 



