92 



NATURAL HISTORY. 



[CH. V. 



a A cell with the cocoon. 



b Ditto. 



c A cell in which the worm has not spun its cocoon; the excrements 



are seen in black dots. 

 d A cell from which the perfect insect has escaped. 



As soon as the mason-bee has discovered, in some 

 old wall, a site suitable for its future habitation, it 

 sets about collecting the material requisite for its 

 construction. This material is a mortar chiefly com- 

 posed of sand. The insect seems to be well aware 

 that all kinds of sand are not equally calculated to 

 produce good cement : x the grains must neither be 

 too large nor too fine. The little creature, there- 

 fore, takes especial care to select, grain by grain, 

 what may suit its purpose ; a few such grains only 

 being apparently contained in a heap of sand, the 

 whole of which a human plasterer would willingly 

 appropriate to the execution of his work. " I can- 

 not understand," says Reaumur, " why the mason- 

 bee did not at once take the whole of its load from that 

 part of the gravel walk on which it had first settled. 

 Having collected a few grains on one spot, it flew 

 off and alighted on another : but, for my part, I 

 could not see that the gravel of one spot differed in 

 the slightest degree from that of the other; both 

 places abounding in large and small grains, inas- 

 much as the whole walk was covered with the same 

 kind of sand. Hence I infer thai this insect pos- 



