1905. | MR. R. I. POCOCK ON A HAINAN GIBBON. 173 
It is known that in some species of Gibbons, e. g. H. leuciscus, 
according to Mr. Hose, the individual variation in colour is con- 
siderable, like unto that which obtaims indeed in some Squirrels 
and Lemurs. But, so far as I am aware, it was not previously 
known that a given individual after reaching maturity may change 
in colour in the way exemplified by Mr. de St. Croix’s specimen. 
This change may be compared to that which takes place in the 
hair of the human head concomitantly as a rule with senescence 
or to that exhibited by some specimens of the Arctic Fox upon 
the approach of winter*. It is not accompanied by any replace- 
ment of coat, nor is it directly attributable to any change in the 
environment or to external agencies. The cause, whatever it may 
be, lies within the organism itself; it is constitutional or subjective, 
and as such may be distinguished by the term “ canescence,” 
from the decoloration or fading which is caused by exposure to 
sunlight or other bleaching agencies. 
In the case of the Hainan Gibbon it is important to note the 
coincidence between the appearance of menstruation and that of 
the colour-change. The former phenomenon began in December 
1903, the latter about February 1904. 
Of the two specimens of this species in the British Museum (both 
of which are jet-black), one is only about two-thirds grown; the 
other, the type, as Mr. Oldfield Thomas states, not quite adult ; 
and since Mr. de St. Croix’s specimen is, on the contrary, full- 
grown, it might be inferred that it is characteristic of the species to 
change from black to grey upon reaching maturity. This, however, 
is not the case; for Mr. de St. Croix informs me that he was 
acquainted in the island of Hainan with another specimen, 
alleged to be a male, which was jet-black, like his own before 
coming to the Zoological Gardens, and had been in captivity 
sufficiently long to justify the belief that it was about twelve 
years old when he last saw it. 
Is the canescence, then, a matter of sex and exhibited only by 
mature females? The balance of evidence seems to be on the 
whole in favour of an affirmative reply to this question. For, 
apart from the change here recorded of the only adult female 
known, it must be remembered that Mr. Swinhoe, in his published 
account of all the information respecting the Hainan Gibbon he 
was able to gather, quotes from the Chinese gazetteer of the 
Kiung Shan district of the island a passage stating that the 
male is black and the female white (P.Z.8. 1870, p. 244, &e.). 
* There are two Arctic Foxes living in the Zoological Gardens at the present time. 
One remains dark-coated throughout the year; the other turns snow-white towards 
the winter. In both the winter coat, whether “white” or “blue,” is replaced 
in the summer by a darkish brown clothing of new hair, which is at its best in 
August, but becomes paler and loses to a large extent its richness of tint as it 
crows. In neither is there an autumn moult comparable in extent to that of the 
spring; and there is no doubt that in the animal which turns white the meta- 
morphosis is effected by the destruction of the pigment in the hairs themselves. This 
bears out Major Barrett-Hamilton’s statement as to what occurs in the Arctie Hare. 
