THE OSMI^ 237 



she would have lodged them in the room which she leaves 

 unoccupied. This string of fifteen appears to be rare; 

 it was the only one that I found. My attempts at indoor 

 rearing, pursued during two years with glass tubes or 

 reeds, taught me that the Three-horned Osmia is not 

 much addicted to long series. As though to decrease the 

 difficulties of the coming deliverance, she prefers short 

 galleries, in which only a part of the laying is stacked. 

 We must then follow the same mother in her migration 

 from one dwelling to the next if we would obtain a com- 

 plete census of her family, A spot of color, dropped on 

 the Bee's thorax with a paint-brush while she is absorbed 

 in closing up the mouth of the tunnel, enables us to rec- 

 ognize the Osmia in her various homes. 



In this way, the swarm that resided in my study fur- 

 nished me, in the first year, with an average of twelve 

 cells. Next year, the summer appeared to be more fa- 

 vorable and the average became rather higher, reaching 

 fifteen. The most numerous laying performed under 

 my eyes, not in a tube, but in a succession of Snail-shells, 

 reached the figure of twenty-six. On the other hand, 

 layings of between eight and ten are not uncommon. 

 Lastly, taking all my records together, the result is that 

 the family of the Osmia fluctuates round about fifteen in 

 number. 



I have already spoken of the great differences in size 

 apparent in the cells of one and the same series. The 

 partitions, at first widely spaced, draw gradually nearer 

 to one another as they come closer to the aperture, which 

 implies roomy cells at the back and narrow cells in front. 



