92 THE NATURAL HISTORY [LETT. 



curiously laid up in an 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 

 nmphibius 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 practice of the aquatic rat to forsake the 

 neighbourhood of the water in the colder months ? 



Though I delight very little in analogous reasoning, knowing 

 how fallacious it is with respect to natural history ; yet, in the 

 following instance, I 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 1 (which by the by is at present a nonde- 

 script 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 

 hawking for flies near the ground, or over the surface of the 

 water. From hence I would conclude that these hinmdines, and 

 the larger bats, are supported by some sorts of high-flying gnats, 

 scarabs, or phalcence that are short of continuance ; and that the 

 short stay of these strangers is regulated by the defect of their 

 food. 



By my journal it appears that curlews clamoured on to 

 October the 31st ; since which I have not seen or heard any. 

 Swallows were observed on to November the third. 



SELBORNE, Dec. 8, 1769. 



1 The little bat appears almost every month in the year ; but I have 

 never seen the large one till the end of April, nor after July. They are 

 most common in June, but never very plentiful. 



