NATURAL HISTORY. 123 



outside wall ; it rises up and is joined to some 

 hole in the side wall of the houses above it." 



" How large is it, Uncle Philip ?" 



" Why, sometimes it is half an inch broad, 

 a quarter of an inch thick, and ten inches 

 long ; all made of clay, so that it is very strange 

 how they manage to join it to the wall with- 

 out its falling down by its own weight while 

 they were building it." 



" And what do you suppose this bridge is 

 for, Uncle Philip T 



" Why, I think there can be no doubt what 

 it is for. When the city has been growing 

 for some time, some of the nurseries will be 

 very high up above the queen's house ; but the 

 labourers have to carry her eggs into them, 

 no matter how far oif they may be. If they 

 carry them through all the streets, they will 

 have to walk as many as fifteen or twenty 

 feet, for it would be five or six feet in a per- 

 fectly straight line, and these streets are very 

 crooked ; but if they make a bridge in the 

 open space in the centre, they can then go 

 from the queen's house over the bridge, and 

 get to the upper nurseries without travelling 

 more than two feet. So they made the bridge 

 to shorten the way, to be sure." 



