THE DEVELOPMENT OF ORGANISMS 813 



of the Cock-of-the-Rock (Rupicola) of tropical South America. 

 "A mossy level spot of earth surrounded by bushes is selected for 

 a dancing-place, and kept well cleared of sticks and stones; round 

 this area the birds assemble, when a cock-bird, with vivid orange- 

 scarlet crest and plumage, steps into it, and, with spreading wings 

 and tail, begins a series of movements as if dancing a minuet ; finally, 

 carried away with excitement, he leaps and gyrates in the most 

 astonishing manner, until, becoming exhausted, he retires, and 

 another bird takes his place." This strikes a note quite different from 

 that which is clearly sounded in the races of lambs and kids, wild 

 foals and asses, or in the various forms of "tig" and "follow my 

 leader" that have been described among monkeys. 



(3) We have suggested that the rubric of play should not include 

 aimless adult movements, which may mean no more than a regular- 

 ised social way of taking exercise, and should not include any form 

 of non-utilitarian display that is connected with courtship, but 

 another restriction may be proposed. It is part of the essence of 

 play that it is not directly useful, but has a prospective value in 

 educating efficiency. Yet not a few animals with abundant spare 

 energy and initiative are known to indulge in occasional adventures 

 which, though they can hardly be called other than playful, have 

 no prospective meaning. Some of the experiments of apes, to which 

 we have already referred, may illustrate this kind of behaviour, and 

 should perhaps be called tricks rather than play. True play is 

 characteristic of a species and is neither occasional nor individual. 

 A naturalist relates that on one occasion, when botanising on the 

 Alps, his dog ceased to follow him on the graduated path, and was 

 seen to choose a more direct slope of hard snow. There he lay down 

 on his back, folded his legs, and slid down like a toboggan. At the 

 foot he looked up at his astonished master and wagged his tail! 

 No conclusion can be based on single instances, however well 

 documented, but we cite this case as an instance of probable mis- 

 interpretation. The observer supposed that the dog had thought out 

 a short cut — an unnecessarily generous view; others have called it 

 a piece of play. But the probability is that it was a casual adventure, 

 such as may be reasonably put to the credit of many a well-endowed 

 animal. But similar instances are known at much lower levels of 

 intelligence. Thus Brehm describes the behaviour of the Spitting 

 Fish, Toxotes jactilator, from the wonderland of Siam. Resting near 

 the surface of the water, it fixes its eyes on an insect; and then, 

 through the almost closed mouth, ejects a drop of water with fatal 

 precision. Meissen, who kept two Jaculators in an aquarium, records 

 that they became so tame that they would take food from their 

 keeper's hand held four or five inches above the water. They be- 

 came accustomed to the sight of strangers and "developed a game 

 with them". "The first case was perhaps accidental; an observer 



