THE PLAY OF ANIMALS. 273 



of these branches and advances along it seriously, with 

 elevated tail, while the others group themselves about 

 him. Soon he gives forth soft single notes, as the lion 

 likes to do when he tests the capacity of his lungs. 

 This sound, which seems to be made by drawing the 

 breath in and out, becomes deeper and in more rapid 

 succession as the excitement of the singer increases. 

 At last, when the highest pitch is reached, the inter- 

 vals cease and the sound becomes a continuous roar, 

 and at this point all the others, male and female, join 

 in, and for fully ten seconds at a time the awful chorus 

 sounds through the quiet forest. At its close the leader 

 begins again with the detached sounds." How can we 

 explain this strange concert? This description gives 

 the impression that it is merely a social game, but how 

 did the animal acquire the instrument on which he 

 plays, the throat thickened as with a goitre? A. von 

 Humboldt says: " The small American monkey chirps 

 like a sparrow, having simply an ordinary hyoid bone, 

 but that of the great ape is a large bony drum. The 

 upper part of the larynx has six compartments, in which 

 the voice is formed. Two of these compartments are 

 nest-shaped and very like the lower larynx of birds. 

 The doleful howl of the ape is caused by the air stream- 

 ing through this great drum, and when we see how 

 large an instrument it is we are no longer surprised at 

 the strength and range of this animal's voice, or that 

 it gives him the name he bears." Such a structure as 

 this must serve some useful purpose, and the idea of 

 courtship suggests itself as the probable use, in the first 

 instance, since it outweighs all other causes for excite- 

 ment. Then its exercise may have come by association 

 to be purely playful. 



Scheitlin says of the cat: "Their pairing time is 



