98 NATURAL HISTORY : 
hybernaculum, artificially formed of grass and 
leaves. At one end of the burrow lay above a 
gallon of potatoes regularly stowed, on which it 
was to have supported itself for the winter. But 
the difficulty with me is how this amphibius mus 
came to fix its winter station at such a distance 
from the water. Was it determined in its choice 
of that place by the mere accident of finding the 
potatoes which were planted there? or is it the 
constant practice of the aquatic rat to forsake the 
neighbourhood of the water in the colder months? 
Though I delight very little in analogous reason- 
ing, knowing how fallacious it is with respect to 
natural history, yet in the following instance [ 
cannot help being inclined to think it may conduce 
towards the explanation of a difficulty that I have 
mentioned before, with respect to the invariable 
early retreat of the hirundo apus, or swift, so many 
weeks before its congeners ; and that not only with 
us, but also in Andalusia, where they also begin to 
retire about the beginning of August. 
The great large bat (which, by-the-by, is at pres- 
ent a nondescript in England, and what I have never 
been able yet to procure) retires or migrates very 
early in the summer : it also ranges very high for 
its food, feeding in a different region of the air; 
and that is the reason I never could procure one.* 
Now this is exactly the case with the swifts; for 
they take their food in a more exalted region than, 
the other species, and are very seldom seen hawk. 
ing for flies near the ground or over the surface of 
the water. From hence I would conclude that these 
* Mr. White first noticed the existence of this species of bat 
in England, 
