282 SCIENCE PROGRESS 



parallel with the outer surface. This burrow is fully half an 

 inch in diameter and a foot in length, taking several days to 

 construct and several more to provision. The consequence of 

 this is that the cells at the farther end are completed and pro- 

 vided with their occupants several days before the last, and, 

 therefore, hatch earlier. It being manifestly impossible for the 

 creature to leave its cell through those occupied by yet 

 undeveloped pupae, the parent bee, in constructing the burrow, 

 makes a second opening at the extreme end, which she seals 

 with grains of sawdust, in a similar fashion to that in which she 

 makes the partitions between the cells. As the bees leave their 

 cocoons, therefore, the way is clear for their exit, except for the 

 sealed end, which is no serious obstacle, even to their un- 

 hardened jaws. 



The construction of the sawdust partitions is worthy of 

 notice, because it is almost precisely the same as that which 

 the honey-bee adopts to form cappings over the cells, a ring of 

 material being first fastened to the side-walls and other grains 

 added on the inside of this, so that, working spirally inwards, 

 the work is finished at the centre. 



Between these two extremes of the Mason-bees building 

 in the simple soil, and the Carpenter-bees tunnelling into solid 

 wood, there are many variations of procedure, and some species 

 save themselves a good deal of labour by utilising materials 

 singularly well adapted for the form which, in most cases, the 

 nests take. One species of Osmia builds in the interior of 

 bramble-stems, removing the pith to form the cells. Unlike 

 those which work in earth or wood, she does not remove the 

 whole of the pith, but carves out separate cells, leaving in situ, 

 where the partitions will come, a ring of pith, to which she 

 afterwards adds sufficient material to fill the centre. Others 

 make use of old shells of various species of land-snail, using 

 each whorl as a separate cell and making partitions of wood- 

 pulp between them. 



A very different procedure, which is a specialised form of the 

 same instinct that induces the Bumble-bee to line its nest with 

 moss, or the honey-bee its hive with gum from trees, is that of 

 the leaf-cutting bees of the genus Megachile and its allies. The 

 common English species is pretty familiar to most people, on 

 account of the neatness with which she cuts semicircular pieces 

 from the leaves of roses. These pieces are used for lining the 

 burrow, which, like that of Anthophora, is made in the earth. 

 A double thickness of leaves is laid round the walls and the 

 divisions between the cells are formed of a circular disc of the 

 same material. Probably the advantage of these linings is that 

 they form an obstacle to the entrance of parasitic animals which 

 live in the soil. Without some such protection worms, for 



