OF SELBORNE 153 



In what space of time these Uttle artists are able to mine 

 and finish these cavities I have never been able to discover, 

 for reasons given above ; but it would be a matter worthy 

 of observation, where it falls in the way of any naturalist to 

 make his remarks. This I have often taken notice of, that 

 several holes of different depths are left unfinished at the 

 end of summer. To imagine that these beginnings were 

 intentionally made in order to be in the greater forward- 

 ness for next spring, is allowing perhaps too much foresight 

 and rerum prudentia to a simple bird. May not the cause 

 of these latehrae being left unfinished arise from their 

 meeting in those places with strata too harsh, hard, and 

 solid, for their purpose, which they relinquish, and go to a 

 fresh spot that works more freely } Or may they not in 

 other places fall in with a soil as much too loose and 

 mouldering, liable to flounder, and threatening to over- 

 whelm them and their labours } 



One thing is remarkable — that, after some years, the old 

 holes are forsaken and new ones bored ; perhaps because 

 the old habitations grow foul and fetid from long use, or 

 because they may so abound with fleas as to become un- 

 tenable. This species of swallow moreover is strangely 

 annoyed with fleas : and we have seen fleas, bed-fleas 

 [pulex irritans)y swarming at the mouths of these holes, like 

 bees upon the stools of their hives. 



The following circumstance should by no means be 

 omitted — that these birds do not make use of their caverns 

 by way of hybernacula, as might be expected ; since banks 

 so perforated have been dug out with care in the winter, 

 when nothing was found but empty nests. 



The sand-martin arrives much about the same time with 

 the swallow, and lays, as she does, from four to six white 

 eggs. But as this species is cryptogame, carrying on the 

 business of nidihcation, incubation, and the support of its 

 young in the dark, it would not be so easy to ascertain the 

 time of breeding, were it not for the coming forth of the 

 broods, which appear much about the time, or rather some- 

 what earlier than those of the swallow. The nesthngs are 

 supported in common like those of their congeners, with 



