OF SELBORNE 135 



and ears they must have large heads to contain them. 

 Large eyes I presume are necessary to collect every ray of 

 light, and large concave ears to command the smallest 

 degree of sound or noise. 



I am, etc. 



It will be proper to premise here that the sixteenth, eighteenth, 

 twentieth, and twenty-first letters have been published already in the 

 Philosophical Transactions : but as nicer observation has furnished 

 several corrections and additions, it is hoped that the republication of 

 them will not give offence ; especially as these sheets would be very 

 imperfect without them, and as they will be new to many readers who 

 had no opportunity of seeing them when they made their first appearance. 



The hirundines are a most inoffensive, harmless, enter- 

 taining, social, and useful tribe of birds: they touch no 

 fruit in our gardens ; delight, all except one species, in 

 attaching themselves to our houses; amuse us with their 

 migrations, songs, and marvellous agility ; and clear our 

 outlets from the annoyances of gnats and other trouble- 

 some insects. Some districts in the south seas, near 

 Guiaquil, 1 are desolated, it seems, by the infinite swarms of 

 venomous mosquitoes, which fill the air, and render those 

 coasts insupportable. It would be worth inquiring whether 

 any species of hirundines is found in those regions. Who- 

 ever contemplates the myriads of insects that sport in the 

 sunbeams of a summer evening in this country, will soon 

 be convinced to what a degree our atmosphere would be 

 choked with them was it not for the friendly interposition 

 of the swallow tribe. 



Many species of birds have their particular lice; but the 

 hirundines alone seem to be annoyed with dipterous insects, 

 which infest every species, and are so large, in proportion 

 to themselves, that they must be extremely irksome and 

 injurious to them. These are the hippoboscae hirundinis, 

 with narrow subulated wings, abounding in every nest; 

 and are hatched by the warmth of the bird's own body 

 during incubation, and crawl about under its feathers. 



A species of them is familiar to horsemen in the south of 

 England under the name of forest-fly ; and, to some, of 



1 See Ulloa's Travels. 



