1905.] MR. R. I. POCOCK OX A HAINAN GIBBON. 173 



It is known that in some species of Gibbons, e. g. H. leuciscus, 

 accoi^ling to Mr. Hose, the individnal variation in colour is con- 

 siderable, like unto that which obtains 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 sj)ecimens 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 

 yeai's old when he last saw it. 



Is the canescence, then, a matter of sex and exhibited only by 

 matvire 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. S. 1870, p. 244, &c.). 



* There are two Arctic Foxes living in the Zoological Gardens at the present time. 

 One remains dark-coated throughout the j'ear ; 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 

 grows. In neither is there an autumu 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 thejnselves. This 

 bears out Major Barrett-Hamilton's statement as to what occurs in the Arctic Hare. 



