INFLEXIBILITY OF INSTINCT. 259 



In the solitary wasps, where the females are much 

 larger than the males, the mother builds a larger cell and 

 provides more food for the former than for the latter. 



The Chalicodoma (one of the mason bees) often lays 

 her eggs in old cells of the previous year. These 

 are of two sizes — large ones, originally built for the 

 females, and small ones for the males. Now, in 

 utilizing old cells, the bee always places male eggs in 

 male cells and female eggs in female cells. If, how- 

 ever, a female cell be cut down so as to reduce the 

 size, then indeed the bee deposits in it a male egg. 



The bees belonging to the genus Osmia* arrange 

 their cells in a row in a hollow stick, or some other 

 similar situation, and it has long been known that in 

 these and similar cases the cells first provisioned, and 

 which are therefore furthest from the entrance, always 

 contain females, while the outer cells always contain 

 males. 



There is an obvious advantage in this, because the 

 males come out a fortnight or more before the females, 

 and it is, of course, convenient that those which have 

 to come out first should be in the cells nearest the 

 door. The bee does not, however, lay all the female 

 eggs first, and then all the male eggs. By no means. 

 She produces altogether from fifteen to thirty eggs, but 

 seldom arranges them in one row ; generally they are 

 in several series, and in every one the same sequence 

 occurs — females further from, and males nearest to, the 

 door. 



For instance, one of M. Fabre's marked bees — one, 

 moreover, of exceptional fertility — occupied some glass 



* Osmia tridentata constitutes an exception to the general rule in 

 this respect, as in some others. 



