The Mason-bees 



bours and in a hurry to lay h-er eggs, found, 

 let us suppose, some suitable cells provisioned 

 by her fellows. There was no time for nest- 

 building and foraging; if she would save her 

 family, she must perforce appropriate the 

 fruit of another's toil. Thus relieved of the 

 tedium and fatigue of work, freed of every 

 care but that of laying eggs, she left a pro- 

 geny which duly inherited the maternal sloth- 

 fulness and handed this down in its turn, in 

 a more and more accentuated form, as gen- 

 eration followed on generation; for the strug- 

 gle for life made this expeditious way of es- 

 tablishing yourself one of the most favour- 

 able conditions for the success of the off- 

 spring. At the same time, the organs of 

 work, left unemployed, became atrophied and 

 disappeared, while certain details of shape 

 and colouring were modified more or less, so 

 as to adapt themselves to the new circum- 

 stances. Thus the parasitic race was definite- 

 ly established. 



This race, however, was not too greatly 

 transformed for us to be able, In certain 

 cases, to trace its origin. The parasite has 

 retained more than one feature of those in- 

 dustrious ancestors. So, for instance, the 

 918 



