position the grouse sleeps securely. But it is difficult to 
understand how it comes to wear this charmed life. 
Surely it is not altogether free from danger. It cannot 
burrow in loose snow without leaving some trace of its 
operations, of which the intelligent beast of prey would 
soon learn the meaning. It can be found by scent if not 
by sight. As it seems to me, the only way of sleeping 
securely in such a case would be to sleep with one eye 
open, ever on the alert against danger. If not, the differ 
ence in the length of the burrow of a few inches, more or 
less, would not present the issue of life or death. 
One does not see, therefore, what safety would come 
from a burrow of a definite length, supposing always that 
the bird were sufficiently covered to be protected from the 
cold and concealed from enemies. But there is a farther 
consideration which leads us to suppose that the exact 
length of the burrow is not determined by the calculations 
of intelligence nor by the good fortune of those who 
unconsciously hit on the right length, and are so pre 
served while others less fortunate are destroyed. Probably 
the length of the burrow is determined by the manner in 
which it is made, for the grouse plunges down from the 
branch of a tree into the snow, and the length of the 
burrow is determined by the strength and the weight of 
the animal ; for we can well believe it exerts all the energy 
of which it is capable. 
In all such cases there is no doubt a competition be 
tween caution in attack, on the one hand, and vigilance 
in avoiding danger on the other, in which sometimes one 
side and sometimes another will win the day; but it is 
difficult to suppose that an exact length of burrow can 
secure perfect safety, while a shorter burrow will involve 
destruction ; and yet that is what Mr. Romanes’ theo 
retical explanation of the phenomenon suggests.