82 BEES AND WASPS [OH. 



which appears to make the overlapping junction of 

 piece to piece more secure. The two ends of the 

 cells are composed of circular, saucer-shaped pieces ; 

 and these seldom, if ever, include any of the marginal 

 serrations : they lie inside the side pieces, and it is 

 thus important that their circumferences shall be 

 as smooth and regular as possible, in order that no 

 gaps may be left to afford entry to small thieves. 

 The bottom pieces are placed with the hollow of the 

 saucer inwards, while those at the top present their 

 convex surface to the space within the cell, thus 

 leaving the upwardly directed concavity ready to 

 receive, or rather to help in forming the bottom of 

 the next cell to be constructed. In the specimen 

 before me there are only two pieces at the bottom, 

 but six at the top : they are all so perfectly circular 

 that with an instrument capable of measuring accu- 

 rately to YijTyth of an inch, I can hardly detect any 

 differences in the diameters of any one : the diameter 

 of the upper bottom one (i.e. that nearest to the cell- 

 cavity, and therefore the smallest), is O'.'M) inch ; that 

 of the innermost lid is 0*33 inch; and that of the 

 topmost lid 0'35 inch. It is most interesting to watch 

 one of these Megachiles at work upon a rose-leaf: 

 having alighted upon a leaflet, she holds on with her 

 legs to the edge of the piece which she wants to cut 

 off and then, by the combined action of the mandibles 

 and chisel-like upper lip, rapidly makes the necessary 



