v SOCIAL HOMES 179 



coverings only for those parts that are more or less 

 exposed. Thus the entrance hole is always obstructed 

 by leaves of paper which close it as much as possible 

 without impeding the way out. Under other circum- 

 stances hornets are at great pains to shelter their 

 combs within a papery coating of many thicknesses, 

 an envelope that constitutes an excellent example of 

 the appearance produced by obtaining strength of 

 walls and large dimensions of comb-tiers by constant 

 exterior additions of puffed-out papery cells. They 

 open on the surface of the nest, where they are very 

 regular, by narrow entrances, always directed down- 

 wards, the object being doubtless to prevent any 

 substance falling from above from penetrating inside. 

 Saussure believes the use of these entrances is to 

 permit the access and circulation of air amid the 

 vacuities of the envelope, for the purpose of drying 

 the papery leaves each time that they are wetted and 

 softened at the surface. The real entrance to the nest 

 is at the inferior extremity, as in other Vespse that 

 nidify in the open atmosphere. 



When hornets take up domicile within a hollow 

 trunk they frequently seem to make no use of the 

 large hole of the tree, but go to the trouble of digging 

 a gallery through some undecayed portion It assumes 

 a winding direction, and probably protects the nest 

 from intrusion. In the opinion of Reaumur, hornets 

 can distinguish a rotten tree, to all appearances 

 healthy. They bore through the sound wood to reach 

 the interior, and gnaw the cavity to suit their con- 

 venience. This penetration of the living matter is 

 difficult, and the hole is never enlarged beyond the 



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