VARIATION AND DIFFERENTIATION. 



15 



5' e 





775 e/5 9/5 /0.I5 11.15 IZ.I5 13.15 I4-.IS 15.15 



Length of Mj in mm. 



Fig. 6. — Diagram showing the regression of the meripodite of leg ill on the meripodite 

 of leg 1. Significance of the lines as in fig. 5. 



There can be no doubt as to the linearity of these regressions. 

 With these general data tables in hand we may proceed at once to the 

 discussion of special topics. 



VARIATION AND DIFFERENTIATION. 



The question with which we have to do in this section is that of the 

 relation of variation to differentiation and morphological specialization. 

 In respect to all of the joints investigated, legs i, ii, and iii are differen- 

 tiated from each other. In the case of leg i this differentiation is of 

 course obvious. We have in the cheliped a part which has developed to 

 a high degree in comparison with its serial homologues, the walking legs. 

 This specialization in respect to size and form is associated with the per- 

 formance of an altogether different set of functions from those of the 

 walking legs. An examination of the following table shows at once that 

 there is a sensible, if less marked, differentiation between corresponding 

 joints of legs ii and iii. 



Table 4. — Comparison of the mean length of corresponding joints in legs II and III. 



[Means from table 1.] 



