Bramble-bees and Others 



swarm finds itself settled at a minimum of 

 expense. 



To conclude this brief account, let us 

 change the zoological setting and, as we have 

 already spoken of the Sparrow,^ see what he 

 can do as a builder. The simplest form of 

 his nest is the great round ball of straw, dead 

 leaves and feathers, in the fork of a few 

 branches. It is costly in material, but can be 

 set up anywhere, when the hole in the wall or 

 the shelter of a tile are lacking. What rea- 

 sons induced him to give up the spherical 

 edifice? To all seeming, the same reasons 

 that led the Osmia to abandon the Snail-shell's 

 spiral, which requires a fatiguing expenditure 

 of clay, in favour of the economical cylinder 

 of the reed. By making his home in a hole 

 in the wall, the Sparrow escapes the greater 

 part of his work. Here, the dome that serves 

 as a protection from the rain and the thick 

 walls that offer resistance to the wind both 

 become superfluous. A mere mattress is suf- 

 ficient; the cavity in the wall provides the 

 rest. The saving is great; and the Sparrow 

 appreciates it quite as much as the Osmia. 



^In an essay, entitled The Sivalloiv and the Sparroiv, 

 not yet translated into English. — Translator's Note, 



230 



