The Dying Huanaco, 321 



well-known instinct in another class of creatures, 

 which has a strong resemblance to that of the 

 huanaco, as I have interpreted it, and which may- 

 even serve to throw a side light on the origin of the 

 huanaco' s instinct. I refer to a habit of some ophi- 

 dians, in temperate and cold countries, of returning 

 annually to hybernate in the same den. 



A typical instance is that of the rattlesnake in 

 the colder parts of North America. On the ap- 

 proach of winter these reptiles go into ' hiding, and 

 it has been observed that in some districts a very 

 large number of individuals, hundreds, and even 

 thousands, will repair from the surrounding country 

 to the ancestral den. Here the serpents gather in 

 a mass to remain in a wholly or semi-torpid condi- 

 tion until the return of spring brings them out again, 

 to scatter abroad to their usual summer haunts. 

 Clearly in this case the knowledge of the hyberna- 

 ting den is not merely traditional — that is, handed 

 down from generation to generation, through the 

 young each year following the adults, and so form- 

 ing the habit of repairing at certain seasons to a 

 certain place ; for the young serpent soon abandons 

 its parent to lead an independent life ; and on the 

 approach of cold weather the hybernating den may 

 be a long distance away, ten or twenty, or even 

 thirty miles from the spot in which it was born. 

 The annual return to the hybernating den is then a 

 fixed unalterable instinct, like the autumnal migra- 

 tion of some birds to a warmer latitude. It is 

 doubtless favourable to the serpents to hybernate in 

 large numbers massed together ; and the habit of 

 resorting annually to the same spot once formed, 



