The Mason-bees 



slide, the thread divides Into four pieces of 

 unequal length. The two longer end In the 

 toothed bevel. They come together in a very 

 narrow groove, which receives the two other, 

 rather shorter pieces. These both end In a 

 point, which, however, is not toothed and 

 does not project as far as the final rasp. They 

 also unite to form a groove, which fits into the 

 groove of the other two, the whole constitu- 

 ting a complete channel or duct. Moreover, 

 the two shorter pieces, considered together, 

 can move, lengthwise. In the groove that re- 

 ceives them ; they can also move one over the 

 other, always lengthwise, so much so that, on 

 the slide of the microscope, their terminal 

 points are seldom situated on the same level. 

 If with our scissors we cut a piece of the 

 inoculating-thread from the living Insect and 

 examine the section under the magnlfylng- 

 glass, we shall see the Inner groove lengthen 

 out and project beyond the outer groove and 

 then go In again In turn, while from the 

 wound there oozes a tiny albuminous drop, 

 doubtless proceeding from the liquid that 

 gives the egg the singular appendage to which 

 we shall come presently. By means of these 

 longitudinal movements of the Inner trench 

 286 



