204 ON THE ORIGIN OF SPECIES 



every angle identically the same with the best measure- 

 ments which have been made of the cells of the 

 hive-bee. 



Hence we may safely conclude that if we could 

 slightly modify the instincts already possessed by the 

 Melipona, and in themselves not very wonderful, this 

 bee would make a structure as wonderfully perfect as 

 that of the hive-bee. We must suppose the Melipona 

 to make her cells truly spherical, and of equal sizes ; 

 and this would not be very surprising, seeing that she 

 already does so to a certain extent, and seeing what 

 perfectly cylindrical burrows in wood many insects can 

 make, apparently by turning round on a fixed point. 

 We must suppose the Melipona to arrange her cells in 

 level layers, as she already does her cylindrical cells ; 

 and we must further suppose, and this is the greatest 

 difficulty, that she can somehow judge accurately at 

 what distance to stand from her fellow-labourers when 

 several are making their spheres ; but she is already 

 so far enabled to judge of distance, that she always 

 describes her spheres so as to intersect largely ; and 

 then she unites the points of intersection by perfectly 

 flat surfaces. We have further to suppose, but this is 

 no difficulty, that after hexagonal prisms have been 

 formed by the intersection of adjoining spheres in the 

 same layer, she can prolong the hexagon to any length 

 requisite to hold the stock of honey ; in the same way 

 as the rude humble-bee adds cylinders of wax to the 

 circular mouths of her old cocoons. By such modifica- 

 tions of instincts in themselves not very wonderful, — 

 hardly more wonderful than those which guide a 

 bird to make its nest, — I believe that the hive-bee 

 has acquired, through natural selection, her inimitable 

 architectural powers. 



But this theory can be tested by experiment. 

 Following the example of Mr. Tegetmeier, I separated 

 two combs, and put between them a long, thick, square 

 strip of wax : the bees instantly began to excavate 

 minute circular pits in it ; and as they deepened these 

 little pits, they made them wider and wider until they 



