436 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Polygon No. lOR. 



Polygon No. lOL. 



10. Propodite of small chela. Polygons No. lOR and lOL. The 

 propodite of the small chela of the Rights is absolutely the least variable 

 of the measurements made on the legs, while the propodite of the great 

 chela of the Rights (Polygon No. 7R) is the most variable of all the 

 organs of the Rights. We have here an illustration of Darwin's law, 

 that a part (the propodite of the great chela) developed to an extraordi- 

 nary degree is more variable than a part (the propodite of the small chela) 

 of ordinary size. This law of variation holds for all the measurements 

 on the great and small chelae of the Rights. 



