206 DIVERSIONS OF A NATURALIST 



male and female, show a brilliant red colouring during 

 the mating season, and the skin and hair of the face is 

 variously coloured, so as to produce a decorative pattern 

 (eyebrows, moustache, beard, nose, all strongly contrasted 

 in colour) in the smaller monkeys, usually more strikingly 

 in the males than in the females. A brilliant emerald- 

 green patch of colour is shown in the hinder part of 

 the body of the male in one species sometimes to be 

 seen at Regent's Park. 



The making of sounds is a capacity possessed by 

 many animals, small and big. Often it seems to have 

 no particular significance, but, as in the case of the 

 " humming " of bees and flies and the " droning " of 

 beetles, is the necessary accompaniment of the vibration 

 of the wings. But many animals make sounds as a 

 " call," either to other individuals of their species, irrespec- 

 tive of sex, or more definitely as signals and appeals to 

 the other sex, just as the luminosity which happens to 

 accompany certain necessary chemical activities in the 

 bodies of the lower animals has become specialized and 

 utilized in the glow-worm and other higher forms as a 

 signal and appeal. The rubbing of rough surfaces 

 against one another is developed into a " stridulating 

 organ " which we find in crickets, locusts, scorpions, 

 spiders, and even in marine Crustacea, and it is often 

 specialized as a sexual appeal. The mere production of 

 sound by tapping against wood is used by the little 

 beetle, the death-watch, as a call, and is responded to 

 by his mate with similar tapping. Such " tapping " is 

 developed into a remarkable rhythmic vibrating sound 

 by the birds called woodpeckers, and has its significance 

 in courtship. But it is chiefly by the inspiration and 

 expiration of air over vibrating cords or membranes 

 called " vocal organs " that animals produce distinctive 



