174 THE INFANCY OF ANIMALS 



because it has developed a prehensile tail whereby it is able 

 to take a secure grip of a bough, leaving the rest of the 

 body free to be instantly uncoiled as the fatal dart on the 

 victim is made. The green colour of the young snake is 

 a protective garment, enabling it to lie concealed among the 

 smaller green boughs. Later, with increased bulk, older 

 and therefore black boughs have to bear the weight of the 

 body, against which a green body would be somewhat 

 conspicuous, or would at any rate excite suspicion. 



Among the deadly pit-vipers (Crotalinae) the young, 

 at any rate of three species — to wit, of the copper-head, 

 Ancistrodon contortrix, the water moccasin {A. piscivorus) 

 and the fer-de-lance {Lachesis lanceolata) — present a very 

 remarkable colour device not present in the adults. When 

 newly hatched, and for some little time after, the tip of 

 the tail, for about an inch, is of a brilUant sulphur yellow ; 

 and it has been found that when food is introduced into 

 the cage of captive specimens, these young vipers set up 

 writhing, twisting movements in this yellow-coloured tail- 

 tip, producing a likeness to a crawling worm or maggot. 

 Thereby, no doubt, small lizards and frogs are lured to 

 their doom, for the rest of the body lies cunningly concealed 

 amid dead leaves and grass. 



The existence of this strange lure is a feature of quite 

 exceptional interest, for it seems to be a device enabling 

 its possessor during its days of inexperience and feebleness 

 to decoy its victims so close up to the head that they may 

 be seized at once and securely. For at this time, when 

 the body is stiU growing, the long fasts, broken by enormous 

 meals, which punctuate the life of the adult, are impossible ; 

 meals must be small and often, and less energy is used 

 when the prey can be brought almost to the very mouth^ 

 than when it has to be tracked down and stalked. Further, 



