YERKES. — VARIATION IN THE FIDDLER CRAB. 425 



2. Tables of Occurrence of Rigid- and Left- Handedness. 



In this connection a statement of the relative frequencies of right- and 

 left-handedness is important. Table III. offers an analysis of two lots 

 of pugilator and pugnax from West Falmouth. Of 9GG males 51.86% 

 were right-handed, 48.14% left-handed. During the summer of 1900 

 additional evidence was obtained on this subject. Over two thousand 

 Fiddlers from the same colony were examined, with the results shown in 

 Table IV. Comparison of these two tables (III. and IV.) indicates that 

 the male Fiddlers are about equally divided into right- and left-handed 

 individuals. The number of females captured was always small, prob- 

 ably because the males remain outside to fight, while the females and 

 immature individuals scurry into the burrows. According to Table IV. 

 the percentage of female pugilators captured was four times as large as 

 that of female pugnax, but for this I am unable at present to offer any 

 explanation. 



3. Polygons of Frequency. 



"We shall now consider the various measurements individually, and 

 examine the Polygons (more accurately Rectangles) of Frequency. 



The polygons are all constructed thus. Each vertical column repre- 

 sents a class, and each of the squares in these columns represents five 

 individuals. Tlie classes are separated by 0.4 mm.* In polygon No. 1 R, 

 for example, the first class is 13.15 mm. and contains one individual ; the 

 second class is 13.55 mm. and contains four individuals. 



1. Frontal breadth. This is the largest and least variable dimension 

 of the twelve under consideration. Polygon No. 1 R represents the 

 distribution, among the various classes, of the right-handed individuals, 

 and No. 1 L that of the left-han<led. Comparison of these two polygons 

 shows a larger number of individuals in the modal class of the Rights 

 than in that of the Lefts, indicating less variability among the right- 

 handed animals. The curves t are both luisymmetrical. This lack of 

 symmetry is probably due, as polygon No. IL especially indicates, to the 

 fact that the curves are really compound. In No. 1 R the modes of the 

 component curves are 15.55 and about 17.55; in No. IL, 15.55 and 

 about 17.15. In both cases the modal class 15.55 contains many more 

 individuals than the mode at 17.15 or 17.55. Professor Davenport has 



* Except in case of the carpopodite and propodite of the small chela, where tliey 

 are separated by 0.2 mm. 



t Tliat is, the curve given by a line passing througli tlie tops of tiie central 

 ordinates of the rectangles. 



