414 H. S. JENNINGS AND K. S. LASHLEY 



shows that the tendency for mates to die continues into this 

 third ten-day period. At the end of the second period (twenty 

 days) there had been left 110 paired hnes and 25 odd ones. There 

 die in the next ten-day period 32 additional Unes, and of these, 

 no less than 30 are mates of those already dead, or of those that 

 die during the present period, while but 2 are mates of those that 

 still live at the end of this period ! 



As one would expect, the chances for such a result, if the dis- 

 tribution of deaths has no relation to the pairing, is infinitesi- 

 mally small. By formula (3), we find that the chance for getting 

 28 pairs is but 0.0000455623. The chance for getting any num- 

 ber whatsoever that deviates from the most probable number 

 (18) as much as does 28 is almost equally small. By our rule (5) 

 we find that the probability that the deviation from 18 will be 

 less than 10 (the observed deviation) is 0.999952421, while the 

 chance that it will be as much as 10 is but 0.00004758. Thus the 

 chances are 21,016 to 1 against there being so great a deviation 

 as was observed, unless the distribution of deaths depends upon 

 the pairing. 



Thus a more complete demonstration that the distribution 

 of deaths depends on the pairing could not be demanded, but 

 the relation is throughout the reverse of that called for by the 

 theory of sexual differentiation. There is not a tendency for 

 one member of the pair to live and for the other to die; on the 

 contrary, there is a most marked tendency for both members to 

 have the same fate. The effects of this tendency show themselves 

 more and more strongly as the lines of progeny successively die 

 out after the pairing. Supposing that such a tendency does not 

 exist, the chances, after seven days, are 39 to 1 against getting so 

 great a deviation as exists ; after twenty days the odds are 445 to 

 1; after thirty days they are 21,016 to 1. 



It appears from the figures given by Miss Cull that there is 

 something in the process of pairing that causes the members of 

 pairs to become alike, so far as survival and death are concerned. 

 This will now be tested by other experiments and in other rela- 

 tions. 



