170 MR. R. I. POCOCK ON A HAINAN GIBBON. [May 16, 
St. Croix, who procured her in the island of Hainan on July 11th, 
1897. She had thus been in captivity nearly six years and seven 
months. On the testimony of natives, her owner believed her to 
be about six weeks old at the time of capture; but since, as he 
affirms, she was already weaned and capable of fending for 
herself in the matter of food, it is probable that she was very 
much older than was supposed. On the assumption that she was 
at least six months old, it may be inferred that the beginning of 
1897 was the approximate date of her birth. 
Menstruation set in at the end of the first week of December 
1903; and taking this as the sign of maturity, coupled with 
the fact that she has not increased appreciably in size since 
her arrival in the Gardens, it may be assumed that she became 
adult when about seven years old. And in view of the close 
aftinity between the various species of Gibbons and the subequality 
in size of full-grown individuals, it may be further inferred that 
about seven years are required on an average for these animals to 
reach maturity * 
Menstruation. 
Very little appears to be known about the menstruation of 
Gibbons. In Chimpanzees, according to Dr. Keith (P. Z.8. 1899, 
p- 297), the discharge is sanguineous in colour, profuse, monthly in 
occurrence, and three days in duration. In our Hainan Gibbon 
it 1s also sanguineous, stains the floor of the cage, and, according 
to her keeper, Mansbridge, who also looked after the Society’s 
historic Chimpanzee ‘“ Sally,” is about the same in quantity 
relatively to the size of the animals as in that ape. The pudendal 
organs are always conspicuous by reason of their turgescence, 
and no very conspicuous change in their condition precedes the 
menstrual discharge. In this particular the Gibbon differs 
markedly from certain Cercopithecide (such as Baboons, Macaques, 
and Mangabeys), and also, to judge from published and verbal 
accounts, considerably, though to a lesser degree, from Chimpanzees. 
With the help of Mansbridge and Robertson, the two keepers of our 
Anthropoid Apes, I recorded the dates of the appearance of the 
discharge during the autumn, winter, and spring. The first noted 
was from Sept. 12 to 14, the second from Oct. 14 to 16, and the 
third from Noy. 19 to 21. During December the animal had a 
severe illness, beginning with an influenza cold and ending with 
diarrhoea, which was accompanied by extreme wasting and weak- 
ness. This illness extended over the time for menstruation, which 
did not appear in December. In January also there was no sign 
of it observable, although by the middle of that month she had 
apparently recovered her normal health. It is probable, I think, 
that the cessation for these two midwinter months was due to 
the illness. But it is by no means impossible that cessation 
during that time of the year is normal. The question can only be 
* Perhaps the Siamang (Symphalangus), which exceeds the other Gibbons in 
dimensions and differs from them in other respects, will be found to be an exception. 
