, 
EVIDENCES OF A DIFFERENTIAL DEATH RATE, ETC. 155 
on the basis of “greater hardship and danger” of the males. 
- *It would seem, rather, to be due to a general lack of resistance, 
both to disease and to harmful environmental factors. 
WHIPPLE (1919, p. 228) has stated the general facts for 
man in the following words: 
“In infancy the death-rate for males exceeds that 
for females by 20%. Between 5 and 25 years of age 
the differences vary considerably in successive years, 
- but average about 10%. Above age 25 the male 
death-rate begins to exceed the female death-rate by 
considerable amounts, and this continues to the age 
of 40, when the excess is 35%. After that, it steadily 
decreases. In old age, the two rates are much alike.” 
II.—SEX-RATIOS AND DEATH-RATES IN FISHES. 
In fishes, the proportions of the sexes are often reported as 
very unequal. This has been particularly true in recent years 
in reports on the Poeciliidae, or top-minnows. In other fam- 
ilies of fishes, also, divergences from the typical, or approxi- 
mately 1:1 ratio of the sexes in the higher animals have been 
“noted. We are indebted largely to DARWIN (1871) and FULTON 
(1890, 1892, 1903) for what little we know of the sex-ratios 
of fishes. 
The reasons for the paucity of literature on the sex-ratios 
of fishes is not far to seek. In sharp contrast with most mam- 
mals, among the lower vertebrates the sexes are indistinguish- 
able at birth. Often a long period elapses before the yourg 
fish has developed secondary characters indicative of the sex 
of the individual. As a consequence the investigator of the 
sex-ratios of fishes has usually contented himself with study- 
in groups of adult fish. No account was taken of juvenile 
mortality. The connotation of the term “‘sex-ratio” then has 
been “‘sex-ratio of collection.” 
In nearly all reported sex-ratios of fishes the populations 
involved were not under experimental conditions. It is there- 
fore clear that the ratios are complicated by unknown factors. 
Most of these ratios varied markedly from the ‘typical sex- 
ratio” in which the sexes are practically’ equal in number. 
Different habitats of the sexes, or differential migration to 
the spawning ground, or sex-peculiarities of behavior at the 
