E. H. J. SCHUSTKR 



209 



but that iieitlicr in the nmle nur in Uiu fL-niiilc is tlie difference of tlie values>of 

 Measurcineat No. 2 so great as of Measui-L'iuciit No. 1. 



It. was f'oinul tliat in tlu- t'eniales tln; valui! of )• Ibr tho Cürreiation between 

 chela index and caiapace longth was less than its probable error aiid tlie regression 

 practically nothing and so neither the correlation tables nor the diagrain of the 

 regression lines are given here. 



V. 



Coniparison uf liegreHnnin and Cürreiation Coefficients. 



TABLE XIX. 



Regr'ession Coefficients of First Oixler. 



Now at first sight it might appear that the greatest diflferences here between 

 deep sea and shallow forms oceur when we consider the regressions of the other 

 Organs on carapaee length. But if we are dealing only with the question of signi- 

 ficant differences, we must note that the probable errors are much larger in these 

 cases. Thus the regression of right chela length on carapaee length for deep sea 

 males nnist be read rS2.93 + '0298, while for the inverse regression of carapaee 

 length on right chela length we have -6033 + -0037. Hence the change in the 

 latter regression froni shallow to deep sea forms although .so much smaller is 

 really more significaut. If, however, we suppose the changes between the regression 

 coefficients for the two forms to bc due, not to the random cbaraeter of the saniples, 

 but to the direct action of natural selection, the greatest absolute differences 

 are clearly in the regressions of the other organs on the carapaee length, or the 

 Suggestion naturally follows that the differentiation between the deep sea and 

 shallow forms is due more to a direct selection of the chela than of the carapaee 

 length. It would be iuteresting to determine whetiier this Suggestion is or is not 

 strengthened when the regression coefficients of higher Orders are investigated. 



Exhibiting all the coi-relation coefficients in a siucrle table we have 



Biometrika ii 



27 



