OFNATURALHISTORY. ^33 



about to undergo. Between the 7th and 8th of the fame month, 

 they threw off their fkins, and were metamorphofed into nymphs. 

 On the 30th of July, thefe nymphs were transformed into flies fimi- 

 lar to their parents. In a range of cells, the worms aie of different 

 ages, and, of courfe, of different fizes. Thofe in the lower cells are 

 older than thofe in the fuperior ; becaufe, after the bee has filled 

 with pafte and enclofed its firft cell, a confiderable time is requifile 

 to colled provifions, and to form partitions for every fucceffive and 

 fuperior cell. The former, therefore, muft: be transformed into 

 nymphs and flies before the latter. Thefe circumftances are appa- 

 rently forefeen by the common mother j for, if the undermoft worm, 

 which is oldeft, and fooneft transformed, were to force its way up- 

 ward, which it could eafily do, it would not only difturb, but infal- 

 libly deftroy all thofe lodged in the fuperior cells. But Nature has 

 wifely prevented this devaftation ; for the head of the nymph, and 

 confequently of the fly, is always placed in a downward diredion. 

 Its firft inftindive movements muft, therefore, be in the fame direc- 

 tion. That the young flies may efcape from their refpedive cells, 

 the mother digs a hole at the bottom of the long tube, which makes 

 a communication with the undermoft cell and the open air. Some- 

 times a fimilar paflage is made near the middle of the tube. By this 

 contrivance, as all the flies inftindively endeavour to cut their way 

 downward, they find an eafy and convenient paflage ; for they have 

 only to pierce the floor of their cells, which they readily perform 

 with their teeth. 



Another fmall fpecies of folitary bees dig holes in the earth to 

 make a convenient habitation for their young. Their nefts are 

 compofed of cylindrical cells fixed to one another, and each of them, 

 in figure, refembles a thimble. Their bottom, of courfe,. is convex 

 and rounded. The bottom of the fecond is inferted into the entry 

 of the firft ; and the entry of the fecond receives the bottom of the 



thir«^. 



