EVIDENCES OF A DIFFERENTIAL DEATH RATE, ETC. 161 
the females. More recently BLEGVAD (1922) has shown in 
the Amphipod Gammarus locusta, and in the Schizopods Mysis 
flexuosa, M. neglecta, and M. inermis, the same sex relation. 
ec.) Insecta. Dr. ELEANOR CAROTHERS has found among 
Orthoptera that while the sexes are produced in practically 
equal proportions, the ratio of the sexes in adult populations 
often varies considerably, due to the lesser yiability of the 
males. When the insects are attacked by disease or by fungus- 
infestation, they are the males who suffer most severely. 
PHIL & NELLIE RAU (1914) have also shown that in the 
Polyphemus moth, the male is much shorter-lived than the 
female. It is only fair to say, however, that they do not find 
this relation universal among the Lepidoptera. Thus, in the 
Cecropia moth, the male is found to live as long or even a 
little longer than the female. It has been suggested by ento- 
mologists, however, that a great many of the insects show 
a difference of longevity of the sexes, in favor of the female. 
IV.—CONCLUSIONS. 
From the foregoing, it appears conclusively to the writer 
that in many diverse groups of animals a lesser viability of 
the males is indicated. What this may be due to, remains to 
be ascertained by future investigation. It appears, however, 
that this differential death-rate cannot be due to deleterious 
influences in the environment to which the two sexes are 
unequally subjected, but is merely the expression of a greater 
stability, or survival-value, in the female of anintals generally. 
1Average annual death-rates for the 0-5 year perod. i 
2 GLovER in his United States Life Tables (U. S, Bur. Census, 1921) has. in, his 
Tables 75 and 76 given data on the differential mortality of the sexes during the first 
year of life in all countries registering births and deaths. His data show death-rates 
for males averaging 120% that of the females. 
Occam’s Razor will exelude the suggestive hypothesis put forward by Hux.iry, in 
the December, 1920, number of the Journal of Ecology to account for reported abnormal 
sex-ratios in Lebistes, a poeciliid Teleost. 
4 These very conclusive demonstrations are to be found in a paper by SCHMIDT, 1920, 
in the Comptes-Rendus des Travaux du Laboratoire Carlsberg, 14me. volume, No. 8, and 
in the more extensive paper by TATuo AIDA, cited in the literature. Since this paper 
was written, WINGE (Jour. Genetics, Vol. XII., No. 2, Oct. 1922) has demonstrated 
cytologically the XX, Xy constitution of Lebistes, and greatly extended the genetical 
studies of SCHMIDT.) 
> Personal communicaton from Miss CAROTHERS. 
