356 DR. F. D. WELCH ON SOME GIBBONS 



A comparison of the external genital organs of the male 

 II. hainan.us with those of Symphalangus syndactylus shows 

 certain differences. In H. hainanus the distal half of the penis, 

 which is covered by mucous membrane, is a dull red, making 

 that organ very conspicuous in the otherwise jet-black coloration. 



In S. syndactylus the penis is black all over, and both it and 

 scrotal bag are very small indeed in proportion to the size of the 

 animal. When hanging the penis is on a level with the ischial 

 callosities, and not above them as in H. hainanus. In S. syndac- 

 tylus the large tuft of long hair growing from below the penis and 

 between the callosities, and spreading out as it runs downwards and 

 backwai-ds between the animal's legs, is most conspicuous, hiding 

 a large part of the ischial callosities from view when the animal 

 is hanging and seen from below. In the skins of Ilylohates in the 

 Museum the hair on the scrotal bag in old males is no longer than 

 that on other parts of the body, except in one very aged H. hoolocic, 

 and in this single specimen it is not neaily so long in proportion as 

 in S. syndactylus ; in skins of *S'. syndactylus males it is very long 

 indeed, as in our living male. 



I might add that in H. hoolock and H. leuciscus the penis is 

 black all over, even in the distal half covered by mucous membrane, 



H. hainanus presents three points distinct from H. hoolock as 

 shown in living specimens. 



When Mr. O. Thomas described the type of H. hainanus (Ann. 

 Nat. Hist. ser. 6, vol. ix. p. 146), he was doubtful as to the 

 validity of the species of Ilylohates ; Mr. Pocock (P. Z. S. 1905, 

 vol. ii. p. 169), from examination of a living female example of 

 H. hainanus, supported the distinctness of the species, and my 

 own observations on our living male confirm this. 



The differences betv/een living specimens of H. hainanus and 

 H. hoolock are as follows : — 



(1) ^. hainanus is more slenderly built in body and limbs 

 than H. hoolock, as I have already pointed out, even when in 

 perfect health. 



(2) In living males the colour of the penis is diff"erent. In 

 H. hainanus the proximal half covered by the skin is black, 

 and the distal half covered by mucous membrane is didl red. In 

 H. hoolock, on the other hand, both proximal and distal halves are 

 black. 



(3) In two living specimens of II. hoolock, male and female, the 

 hair on the crown of the head lay quite smooth and there was no 

 erect crest whatever. In the male H. hainanus now alive the 

 hair on the crown of the head stands erect in a crest, as it 

 did in the female, as Mr. Pocock remarks (P. Z. )S. 1905, vol. ii. 



p. 175). 



I might add that the hair on the crowns of the living specimens 

 of H. agilis and H. leuciscus is quite flat and there is no erect 

 crest whatever. H. haina,nus is the only species that I have yet 

 seen which has an erect crest on the crown ; it also has a short 

 beard on the chin. 



