300 NATURAL HisroRy 



veral holes of different depths are left un- 

 finished 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 reriim prudcntia to 

 a simple bird. May not the cause of these 

 laiebrcB 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 

 founder, and threatening to overwhelm 

 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 untenantable. This 

 species of swallow moreover is strangely 

 annoyed with fleas : and we have seen fleas, 



