High and low Dimorphism. 



315 



between the g-eneral size of tlie male and the degree of develöpment 

 of the chela by the curve of averag-e growth giveu in Diagram 1 

 which was made from measurements on 496 males taken at random 

 duriug the breeding- seasou. 



Chela breadth iu millimeters. 



Textfigure 4 (Diagram 1). 

 The curve is constructed from Table 1 in Appendix 2 (see below 

 page 338) bv drawing a line through the average chela breadth asso- 

 ciated with each particular carapace length, and the shape of the 

 curve expresses clearly the fact that in crabs between 15 and 

 19 mm. carapace length there is no average increase of breadth in 

 the chela, and that the iucrease in breadth is more rapid in crabs 

 atter 19 mm. carapace length than between 9 and 15 mm. The same 

 thiug applies to the average chela length, so that it is growth in the 



