354 DR. F. D. WELCH ON SOME GIBBONS 



genital organs. On arrival in December 1907 it was in good 

 health and measured about 14 inches from crown to ischial 

 callosities, and there were then no signs of a scrotal bag, the skin 

 between penis and ischial callosities being quite flat. About the end 

 of March 1909 a scrotal bag gradually formed, and by the first 

 week in July 1909 this could be seen quite easily when the animal 

 was at the opposite side of the cage with its hind legs separated. 

 The scrotal bag had then reached its? present size and appearance, 

 being just over an inch long with a broad base and tapering 

 rapidly towards a point, thickly covered all over with short black 

 hair, and placed well above and in front of the anterior ends of the 

 ischial callosities, there being a space over half an inch between the 

 callosities and its posterior surface. The scrotal bag is not at all 

 pendulous, and the long axis runs downwards and forwards. At 

 that time, July 1909, the animal's height, measured against the 

 bars when sitting, was 16 inches. It was impossible to measure 

 this male out of the cage or to handle it, and as all Hylohates 

 specimens stoop when sitting, the real height of the animal when 

 hanging at full length was probably about 1 inch more than this. 

 The measurement against the bars was repeatedly taken to ensure 

 accuracy. Only one male H. hainanus has been exhibited in the 

 Gardens before, a younger animal, to the skin of which, now in 

 the Natural History Museum, I shall refer later. 



Retention of the testicles, either within the abdominal cavity or 

 in the inguinal canal, is a common human abnormality. One or 

 both testicles may be thus retained, and in some cases they descend, 

 later in life, into the scrotal bag. I certainly do not think that this 

 male R. hainamcs was abnormal, but that the absence of a scrotal 

 bag before March 1909 was the normal condition in the genus 

 and species, and my reasons for this opinion are as follows : — 



The male 11. leuciscus from Borneo, now in the Gardens, had 

 on arrival no scrotal bag, and in December 1 909 I made a careful 

 digital examination of the external genital organs. The skin 

 between the penis and ischial callosities was slightly wrinkled, but 

 would not stretch when pulled, and did not hang down when the 

 animal was standing erect. There was nothing to be felt under 

 the skin between penis and callosities which I could say with 

 perfect certainty were the testicles, and consequently these organs 

 must be exceedingly small in proportion to the size of the animal. 

 This H. leuciscus was in good health on arrival and has continued 

 so, and at the present time (November 1910) there is no sign of a 

 scrotal bag. The animal at present measures 14 inches from 

 crown to callosities when sitting. Exactly the same condition 

 of no scrotal bag or testicles to be easily felt was found in two 

 other males I examined, one 14 inches high from crown to 

 callosities, the other 1 1 inches. This condition in these four Hylo- 

 hates males was very different from that of a young Anthropo- 

 pithecus troglodytes I examined, as in this latter male the scrotal 

 bag was large and well developed, being seen quite easily at a 

 distance of fifteen feet, and both testicles could be felt easily. 



