418 PROCEEDINGS OF THE AMERICAN ACADEMY. 



desire to use them, they will be placed iu the Library of Harvard Uni- 

 versity, subject to the order of either the librarian or the writer. 



Through the kindness of Mr. Alexander Agassiz and the authorities 

 of the United States Fish Commission Station at Wood's Hole, Massa- 

 chusetts, I was permitted to occupy, during a part of the summer of 

 1899, one of the tables in the Fish Commission Laboratory controlled 

 by the Museum of Comparative Zoology. I desire to thank them for 

 the privilege, and also Professor H. C. Bumpus, Director of the Labo- 

 ratory, for facilities in collecting material and for many courtesies which 

 made work pleasant. To Professor E. L. Mark I am indebted for 

 suggestions and assistance iu the arrangement of this report ; to Pro- 

 fessor C. B. Davenport I owe the knowledge and interest which led me 

 to the problems, and to him I am also indebted for invaluable assistance 

 in the prosecution of the work. 



II. Problems. 



The original purpose of this work was the determination of place- 

 modes for Gelasimus pugilator of West Falmouth, Mass. Examination 

 of the material for measurement and consideration of the probable value 

 and significance of various dimensions led to the inclusion of several 

 other problems. For it seemed advisable to select for the determina- 

 tion of place-modes such measurements as would be likely to contribute 

 data for problems of adult form, of development, and of function. 



The male Fiddlers are either right- or left-handed, one chela being 

 enormously developed, the other small. The proportions of right- and 

 left-handed animals will be considered later. In the females the chelae 

 are nearly equal. One immediately asks: (1) What is the meaning of 

 this condition in the males ? (2) What relation does the size of the 

 chela bear to the other body measurements ? (3) What determines 

 whether an animal shall be ricrht- or left-handed ? These are some of 

 the problems which, it was hoped, might be at least partially solved by 

 a quantitative study of variation ; for unquestionably this method can 

 supplement in important ways histological and physiological studies. 



It was my purpose to measure equal numbers of the two species of 

 Fiddlers, Gelasimus pugilator and G. pugnax, found in the vicinity of 

 Wood's Hole,* selecting equal numbers of males and females fi-om each 

 of the two species. But the task of measuring was slow, and the time 

 then available for the work was exhausted before its completion. This 



* G. minax does not occur in the vicinity. 



