" (W. Heape,
"Menstruation and Ovulation of _Macacus rhesus_," _Philosophical
Transactions_, 1897; id. "The Sexual Season of Mammals,"
_Quarterly Journal Microscopical Science_, 1900.)
Except, however, in one important respect, with which we shall presently
have to deal, few attempts have been made to demonstrate any annual
organic sexual rhythm. The supposition of such annual cycle is usually
little more than a deduction from the existence of the well-marked
seasonal sexual rhythm in animals. Most of the higher animals breed only
once or twice a year, and at such a period that the young are born when
food is most plentiful. At other periods the female is incapable of
breeding, and without sexual desires, while the male is either in the same
condition or in a condition of latent sexuality. Under the influence of
domestication, animals tend to lose the strict periodicity of the wild
condition, and become apt for breeding at more frequent intervals. Thus
among dogs in the wild state the bitch only experiences heat once a year,
in the spring. Among domesticated dogs, there is not only the spring
period of heat, early in the year, but also an autumn period, about six
months later; the primitive period, however, remains the most important
one, and the best litters of pups are said to be produced in the spring.
The mare is in season in spring and summer; sheep take the ram in
autumn.
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