SAND-MARTINS. . 195 



and skill to a simple bird. May not the cause of 

 these latebrte 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 threaten- 

 ing 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, bed-fleas, (pulex irritansj 

 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 ex- 

 pected ; 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 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 ap- 

 pear much about the time, or rather somewhat earlier 

 than those of the swallow. The nestlings are sup- 

 ported, in common, like those of their congeners, with 

 gnats and other small insects, and sometimes they are 

 fed with libellulce, (dragon-flies,) almost as long as 

 themselves. In the last week in June, we have seen 

 a row of these sitting on a rail, near a great pool, as 

 o 2 



