r>9G 



THE AMERICAN NATURALIST [Vol. XLVIII 



of inbreeding in brother X sister mating is the same as for self- 

 fertilization, save that it lags one generation behind the latter; 

 thus the coefficient for the fourth generation of self-fertilization 

 is the same as that for the fifth of brother X sister mating. Pearl 

 (1, p. 592) has already pointed out that in cousin mating the 

 coefficient is one-half that for brother X sister, with a lag of one 

 generation; as compared with self-fertilization the lag is two 

 generations. No such simple relation is apparent between the 

 proportions of homozygotes resulting from the diverse methods 

 of breeding, though possibly such may yet be discovered. 



H. S. Jennings 



PAPERS CITED 



ing.' This Journal, XLVII, October, 1913, pp. 577-614. 



2. . On the results of inbive.ling a Memlelism population; a correction 



and extension of previous conclusions. This Journal, XLVIII, Jan- 

 uary, 1914, pp. 57-62. 



This Journal^ XLVIII, August, 1914, pp. 491^94. 

 4 Jennings, H. S. Production of pure homozygotic organisms from hetero- 

 zygotes by self-fertilization. This Journal, XLVI, August, 1912, pp. 

 487-491. 



A SHORT-CUT IN THE COMPUTATION OF CERTAIN 

 PROBABLE ERRORS 

 In his handbook of statistical methods, on p. 38, Dr. C. B. 

 Davenport 1 gives a short method for the calculation of the prob- 

 able errors of some of the commonest statistical constants, in a 

 table of logarithmic formula?. It would seem that the simple 

 and obvious short-cut involved has not been given the attention 

 it deserves in connection with non-lo<j';iri1hmic calculation. The 

 logarithmic formulae are as follows : 2 



(1) log E A = log .6745 + Iog a - \ log n [^since E A = .6745 ~= J, 



log E 9 - log E A - * log 2 since E„ = .6745 

 (2) L 



