202 SAND-MARTINS. 



intentionally made, in order to be in the greater 

 forwardness for next spring, is allowing, perhaps, 

 too much foresight and rerum prudentia to a 

 simple bird. May not the cause of these latebra 

 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 

 foetid 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, bed-fleas (pulex 

 irritans,) swarming at the mouths of these holes, 

 like bees on 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 cryp- 

 togame, carrying on the business of nidification, 

 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 somewhat earlier than those of the 

 swallow. The nestlings are supported in common 



