CHAPTER VII 



ECONOMY OF ENERGY 



VI/'HAT stimulus does the insect obey when 

 ^^ it employs the reserve powers that 

 slumber in its race? Of what use are its in- 

 dustrial variations? The Osmia will yield us 

 her secret with no great difficulty. Let us ex- 

 amine her work in a cylindrical habitation. I 

 have described in full detail, in the foregoing 

 pages, the structure of her nests when the 

 dwelling adopted is a reed-stump or any other 

 cylinder; and I will content myself here with 

 recapitulating the essential features of that 

 nest-building. 



We must first distinguish three classes of 

 reeds according to their diameter: the small, 

 the medium-sized and the large. I call small 

 those whose narrow width just allows the Os- 

 mia to go about her household duties without 

 discomfort. She must be able to turn where 

 she stands in order to brush her abdomen and 

 rub off its load of pollen, after disgorging the 

 honey in the centre of the heap of flour al- 



ax3 



