120 A NEW THEORY OF EVOLUTION. 



One variety of the Mason-bee is solitary, 

 and builds its cell of small angular stones 

 laid in courses and cemented together with 

 mortar. Six to ten cells are built together 

 and then covered with a dome as protection 

 from the weather. 



Another variety is to some extent sociable. 

 The cells are built, sometimes in thousands, 

 in an irregular group, without any plan, each 

 mother occupying herself only about her own 

 cells. When, however, all the eggs are laid 

 the colony unites to build a dome that covers 

 the whole group. 



Such are a few of the singular habits of 

 these insects ; but there are many others, 

 with instincts equally wonderful and dis- 

 tinct, for which we must refer the reader 

 to Monsieur Fabre's charming book, ' Insect 

 Life.' 



The comb of the hive-bee was, according 

 to Darwin, evolved from the somewhat ir- 

 regular cells of the Melipona domestica (a 

 Mexican species intermediate in structure 

 between the humble-bee and the hive-bee), 

 which constructs nearly cylindrical cells for 

 its larva. 



According to Darwin, this structure was 

 ultimately developed by the accumulation 

 of small improvements into the comb of 



