6 Mr. Spence on the Italian Mode, 8^c. 



and the ascertaining the extreme width at which they cease to have 

 effect ; how far mere horizontal threads are as effectual as a net- 

 work of both vertical and horizontal ones, &c. : and by observations 

 on these points and various others which will suggest themselves, 

 and especially by carefully watching the motions of the flies on the 

 outside of the windows, as to their approaching or avoiding the net, 

 and their different conduct when a thorough light is admitted, there 

 can be little doubt that some approach mety be made to a solution of 

 the question, whether their movements in this case are influenced by 

 pure instinct or by reason and calculation, and thus some valuable 

 additions be made to the metaphysics of entomology, that branch of 

 the science which, as I began by observing, has been hitherto so 

 much neglected, but is in itself so highly interesting. 



Another point, too, to which it seems desirable to pay attention is 

 as to the precise species of flies which have this dread of passing 

 through a net. It seems probable, from the facts stated, that not 

 merely the common house-fly (Mmsca domestica), which chiefly swarms 

 in our apartments, but the other species of the same genus which in 

 smaller number intermingle with them, as well as Stomoxys calci- 

 trans, which from its attacks on our legs is often a greater pest, and, 

 indeed, the dipterous tribes in general, are all equally deterred from 

 traversing this imaginary boundary. But before this suj^position 

 can be fully adopted, more exact observations than have yet been 

 made require to be instituted, and it would also be desirable to have 

 similar experiments made as to the house-flies of America and other 

 hot countries, in which it is probable that in the same way as our 

 common sparrow {Fringilla domestica, Linn.) is replaced in Italy by 

 another species {F. cisalpina, Temm.), which to an ordinary observer 

 seems identical with ours, but is really distinct, the prevfilent house- 

 fly may be a species nearly allied to Musca domestica, which it re- 

 places, but distinct from it. 



I shall conclude my remarks with briefly adverting to the con- 

 nexion, alluded to in the introductory paragraphs, which has been 

 unexpectedly found to exist between this subject and a topic of clas- 

 sical criticism. On mentioning the facts above recorded, when I 

 first learnt them at Florence, to my family circle, my eldest son ob- 

 served that he recollected a passage in Herodotus in which a similar 

 statement was made as to gnats, and fetching the volume, he pointed 

 out the chapter in which the father of history distinctly says, that 

 certain Egyptian fishermen defended themselves at night from the 

 gnats by covering their beds vath the nets which they had used in 

 the day for fishing, and through which these insects, though they bit 

 through linen or woollen, did not even attempt to bite. But as to 



