The Leaf-cutters 



same time they assure me that any such inno- 

 vation is sudden and not gradual. Nothing 

 prepares the innovations, nothing improves 

 them or hands them down; otherwise a 

 selection would long ago have been made 

 amid the diversity of foliage; and the shrub 

 recognized as the most serviceable, especially 

 when it is also plentiful, would alone supply 

 all the building-materials needed. If heredity 

 transmitted industrial discoveries, a Mega- 

 chile who thought of cutting her disks out of 

 pomegranate-leaves and found them satisfac- 

 tory ought to have instilled a liking for simi- 

 lar materials into her descendants; and we 

 should to-day find Leaf-cutters faithful to the 

 pomegranate-leaves, workers who remained 

 exclusive in their choice of the raw material. 

 The facts refute these theories. 



People also say: 



"Grant us a variation, however small, in 

 the insect's industry; and that variation, ac- 

 centuated more and more, will produce a new 

 race and finally a fixed species." 



This trifling variation is the fulcrum for 

 which Archimedes clamoured in order to lift 

 the world with his system of levers. The 

 Megachilcs offer us one and a very great one: 



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