2o6 THE WONDERS OF INSTINCT 



the plasterer, who rejects plaster injured by damp. 

 We shall see presently how the insects that build under 

 shelter avoid this laborious macadam-scraping and give 

 the preference to fresh earth already reduced to a paste 

 by its own dampness. When common lime answers our 

 purpose, we do not trouble about Roman cement. Now 

 Eumenes Amedei requires a first-class cement, even 

 better than that of the Chalicodoma of the Walls, for 

 the work, when finished, does not receive the thick 

 covering wherewith the Mason-bee protects her cluster 

 of cells. And therefore the cupola-builder, as often as 

 she can, uses the highway as her stone-pit. 



With the mortar, flints are needed. These are bits 

 of gravel of an almost unvarying size — that of a pepper- 

 corn — but of a shape and kind differing greatly, accord- 

 ing to the places worked. Some are sharp-cornered, 

 with facets determined by chance fractures; some are 

 round, polished by friction under water. Some are of 

 limestone, others of silicic matter. The favorite stones, 

 when the neighborhood of the nest permits, are little 

 nodules of quartz, smooth and semitransparent. These 

 are selected with minute care. The insect weighs them, 

 so to say, measures them with the compass of its 

 mandibles and does not accept them until after recog- 

 nizing in them the requisite qualities of size and hardness. 



A circular fence, we were saying, is begim on the bare 

 rock. Before the mortar sets, which does not take long, 

 the mason sticks a few stones into the soft mass, as 

 the work advances. She dabs them half-way into the 

 cement, so as to leave them jutting out to a large extent, 



