The Dying FTuanaco. 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 certaim 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 along 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, 
Y 
