discharge in a species
of cebus in Paraguay, while Raciborski observed in the Jardin des Plantes
that the menstrual haemorrhage in guenons was so abundant that the floor of
the cage was covered by it to a considerable extent; the same variety of
monkey was observed at Surinam, by Hill, a surgeon in the Dutch army, who
noted an abundant sanguineous flow occurring at every new moon, and
lasting about three days, the animal at this time also showing signs of
sexual excitement.[90]

The macaque and the baboon appear to be the non-human animals, in which
menstruation has been most carefully observed. In the former, besides the
flow, Bland Sutton remarks that "all the naked or pale-colored parts of
the body, such as the face, neck, and ischial regions, assume a lively
pink color; in some cases, it is a vivid red."[91] The flow is slight, but
the coloring lasts several days, and in warm weather the labia are much
swollen.

Heape[92] has most fully and carefully described menstruation in monkeys.
He found at Calcutta that the _Macacus cynomolgus_ menstruated regularly
on the 20th of December, 20th of January, and about the 20th of February.
The _Cynocephalus porcaria_ and the _Semnopithecus entellus_ both
menstruated each month for about four days. In the _Macaci rhesus_ and
_cynomolgus_ at menstruation "the nipples and vulva become swollen and
deeply congested, and the skin of the buttocks swollen, tense, and of a
brilliant-red or even purple color. The abdominal wall also, for a short
space upward, and the inside of the thighs, sometimes as far down as the
heel, and the under surface of the tail for half its length or more, are
all colored a vivid red, while the skin of the face, especially about the
eyes, is flushed or blotched with red." In late gestation the coloring is
still more vivid. Something similar is to be seen in the males also.

Distant, who kept a female baboon for some time, has recorded the dates of
menstruation during a year. He found that nine periods occurred during the
year. The average length between the periods was nearly six weeks, but
they occurred more frequently in the late autumn and the winter than in
the summer.[93]

It is an interesting fact, Heape noted, that, notwithstanding
menstruation, the seasonal influence, or rut, still persisted in the
monkeys he investigated.

In the anthropoid apes, Hartmann remarks that several observers have
recorded periodic menstruation in the chimpanzee, with