Bramble-bees and Others 



regarded as ellipsoids formed by a revolution 

 around the major axis. The volume of one 

 of these solids is expressed in the following 

 formula : 



i;rab', 



in which 2a is the major axis and ib the 

 minor axis. 



Now, the average dimensions of the co- 

 coons of the Three-horned Osmia are as fol- 

 lows : 



2a — 13 mm.,^ 2^ = 7 mm.^ in the females; 

 2a = 9 mm.,^ 2^ = 5 mm.* in the males. 



The ratio therefore between 13 X 7 X 7 

 = 637 and 9X5X5 =225 will be more or 

 less the ratio between the sizes of the two 

 sexes. This ratio is somewhere between 2 toi 

 and 3 to I. The females therefore are two 

 or three times larger than the males, a propor- 

 tion already suggested by a comparison of the 

 mass of provisions, estimated simply by the 

 eye. 



^.507 inch. — Translator's Note. 

 2.273 inch. — Translator's Note. 

 3.351 inch. — Translator's Note. 

 ^.195 inch. — Translator's Note. 



no 



