The Dying FIuanaco, 2a 
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, 
