THE OSMLE 241 



at random. Why this mixture in the series of cocoons 

 of a Bee closely related to the Horned Osmia and the 

 Three-horned Osmia, who stack theirs methodically by 

 separate sexes in the hollow of a reed? What the Bee 

 of the brambles does cannot her kinswomen of the reeds 

 do too? Nothing, so far as I know, explains this fun- 

 damental difference in a physiological act of primary im- 

 portance. The three Bees belong to the same genus; 

 they resemble one another in general outline, internal 

 structure and habits; and, with this close similarity, we 

 suddenly find a strange dissimilarity. 



There is just one thing that might possibly arouse a 

 suspicion of the cause of this irregularity in the Three- 

 pronged Osmia's laying. If I open a bramble-stump in 

 the winter to examine the Osmia's nest, I find it impos- 

 sible, in the vast majority of cases, to distinguish posi- 

 tively between a female and a male cocoon : the difference 

 in size is so small. The cells, moreover, have the same 

 capacity: the diameter of the cylinder is the same 

 throughout and the partitions are almost always the same 

 distance apart. If I open it in July, the victualing- 

 period, it is impossible for me to distinguish between the 

 provisions destined for the males and those destined for 

 the females. The measurement of the column of honey 

 gives practically the same depth in all the cells. We find 

 an equal quantity of space and food for both sexes. 



This result makes us foresee what a direct examination 

 of the two sexes in the adult form tells us. The male 

 does not differ materially from the female in respect of 

 size. If he is a trifle smaller, it is scarcely noticeable, 



