The Distribution of the Sexes 



larlty 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 impossible, 

 in the vast majority of cases, to distinguish 

 positively 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 through- 

 out and the partitions are almost always the 

 same distance apart. If I open It in July, 

 the victualling-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 provided for both the males 

 and the females. 



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, 

 whereas, in the Horned Osmia and the Three- 

 horned Osmia, the male Is only half or a 

 third the size of the female, as we have seen 

 from the respective bulk of their cocoons. In 



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