The Mother Decides the Sex 



ber, a second partition of pure resin and, 

 lastly, a smaller cocoon in a narrow chamber. 

 The inequality of the two cells is the neces- 

 sary consequence of the shape of the shell, 

 whose inner space gains rapidly in width as 

 the spiral gets nearer to the orifice. Thus, 

 by the mere general arrangement of the home 

 and without any work on the Bee's part be- 

 yond some slender partitions, a large room is 

 marked out in front and a much smaller 

 room at the back. 



By a very remarkable exception, which I 

 have mentioned casually elsewhere, the males 

 of the genus Anthidium are generally larger 

 than the females; and this is the case with 

 the two species in particular that divide the 

 Snail's spiral with resin partitions. I col- 

 lected some dozens of nests of both species. 

 In at least half the cases, the two sexes were 

 present together; the female, the smaller, oc- 

 cupied the front-cell and the male, the hig- 

 her, the back-cell. Other cells, which were 

 smaller or too much obstructed at the back 

 by the dried-up remains of the mollusc, con- 

 tained only one cell, occupied at one time by 

 a female and at another by a male. A few, 

 lastly, had both cells inhabited now by two 



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