320 



Geoffrey Smith 



chela of the smaller males is quite disproportionately reduced 

 (Figs. 8 and 9). This is iudicated in the foUowing diagram 3, which 

 is constructed from Table 2, iu Appendix 2. 



Chela length in mm. 

 ß 



V 



03 



Textfigure 9 (Diagram 3). 



It is here seen that the line of actual growth A of the chela rela- 

 tively to the body length, falls altogether outside the line of pro- 

 portionate growth B. I have been unable to determine whether 

 the high and low forms constitute a bimodal curve of frequency, 

 but this appears highly probable from the fact that several species 

 have been made out of them diÖeriug in the degree of development 

 of the chela. 



C. Orchcstia Danvinn. According to Fritz Müller (1) the males 

 of this species are sharply divided into two categories which ditler 

 in respect to the form and degree of development of the chela. If 

 the males of both these forms were really adult members of the 

 same species we jirobably have here a case of high and low 

 dimori)liism. Della Valle however in bis Mouograph on the 

 Gammarini of the Bay of Xaples throws doubt on Müller's Obser- 

 vation, but not with very sufflcient reason. 



D. Forficidd üuriciildria. The classical case of high and low 

 dimorphism in the males of this si)ecies was described by Bateson & 

 Bkindley (2) from the Farne Islands. The 583 males, measured in 

 respect of the forceps, feil into a markedly bimodal curve, and 

 altliough measuremeuts to show the corrclation of this character with 



