OSMIA. 297 



sand or earth mixed with minute pebbles, scarcely lar- 

 ger than grains of sand, or raspings of wood combined 

 in the same manner, with a secretion which they emit, 

 and of which they form their cells. The instinct of the 

 creature prompts it to be speedy in the operation, as the 

 material, like plaster of Paris, dries very rapidly to a 

 hard substance. Whether they have the power of 

 softening the edges as the manufacture of the cell pro- 

 ceeds is not known, nor whether, as they add the 

 material, it instantaneously consolidates itself, but the 

 colour of the structures themselves would indicate a 

 simultaneous mixture. This could not be the case, if 

 the mortar or mixture were formed away from the domicile 

 and brought home in little pellets, each being added 

 upon the insects' arrival, although they obtain it all from 

 the same spot, whence arises its uniformity in colour,, 

 and they are speedy in the formation of their nests. 

 These cells are rather rough externally, according to the 

 nature of the material of which they are composad, but 

 they are very smooth within. The nature of the cells 

 varies with the places of their deposit, which is dependent 

 upon the idiosyncrasy of the species. Thus, those which 

 construct their cells in wood, form them of moistened 

 particles of wood, and those which make them in cavi- 

 ties of any kind, in the earth, beneath stones, or within 

 empty snail-shells, make a mortar of earth and sand 

 and small pebbles. Some are strictly uniform in the 

 selection of the material wherein they build, but others 

 are perfectly indifferent to its locality, and adopt either 

 earth or wood, and sometimes the mortar of walls, sand- 

 banks or chalk cliffs. According to the nature or the 

 size of the receptacle which they select, is the adjust- 

 ment- of these cells. Where the cavity is restricted they 



