244 THE WONDERS OF INSTINCT 



chambers of the nest which she owes to chance, deposit 

 unerringly the sex for which those chambers were orig- 

 inally built ; and this happens however small the number 

 of chambers to be filled. 



When the mother herself founds the dwelling, when 

 she lays the first rows of bricks, the females come first 

 and the males at the finish. But, when she is in the 

 presence of an old nest, of which she is quite unable to 

 alter the general arrangement, how is she to make use 

 of a few vacant rooms, the large and small alike, if the 

 sex of the egg be already irrevocably fixed? She can 

 only do so by abandoning the arrangement in two con- 

 secutive rows and accommodating her laying to the 

 varied exigencies of the home. Either she finds it im- 

 possible to make an economical use of the old nest, a 

 theory refuted by the evidence, or else she determines at 

 will the sex of the egg which she is about to lay. 



The Osmiae themselves will furnish the most conclusive 

 evidence on the latter point. We. have seen that these 

 Bees are not generally miners, who themselves dig out 

 the foundation of their cells. They make use of the old 

 structures of others, or else of natural retreats, such as 

 hollow stems, the spirals of empty shells and various hid- 

 ing-places in walls, clay or wood. Their work is con- 

 fined to repairs to the house, such as partitions and 

 covers. There are plenty of these retreats; and the in- 

 sects would always find first-class ones if it thought of 

 going any distance to look for them. But the Osmia 

 is a stay-at-home: she returns to her birthplace and 



