CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE 

 MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE. 

 E. L. MARK, DIRECTOR. — No. 119. 



A STUDY OF VARIATION IN THE FIDDLER CRAB 

 GELASIMUS PUGILATOR LATR. 



By Robert M. Yerkes. 



Presented by E. L. Mark, February 13, 1901. Received March 4, 1901, 



Contents. 



Page 



I. Introduction 417 



II. Problems •. ... 418 



III. Methods and Material 419 



IV. Results 423 



1. Tables of Means, Modes, Standard Deviations, and CoefScients 



of Variability 423 



2. Tables of Occurrence of Right- and Left-Handedness 425 



3. Polygons of Frequency 425 



4. Table of Correlation of Meropodites of Chelae 438 



V. Discussion of Results 440 



VI. Summary 441 



Bibliography , 442 



I. Introduction. 



This study was undertaken to get light on some minor problems of 

 variation, and to furnish records for future reference. 



The matter of future reference seems to me of special importance, for 

 it is evident that with records of the variations of a race during stated 

 intervals available, the course and progress of evolution may be more 

 or less accurately traced. Davenport ('99) has emphasized the need of 

 the collection and filing of statistics of variation, especially of Place- 

 Modes ; and it was in response to his plea for this kind of work that I 

 undertook to determine some place-modes for one of the Fiddler Crabs 

 (Gelasimus pugilator) of a certain region. 



In order to make the records of measurements together with my com- 

 putations and interpretations available for any who may, in the future, 

 VOL. XXXVI, — 27 



