ON THE FORM OF BEES' CELLS. 357 



judge whether the walls and ceiling of a room were truly at 

 right angles to each other. And so in the case proposed. To 

 this guess two objections have been made, the first, that most 

 if not all hymenoptera have similar eyes, but do not make 

 similar cells ; the second, that there is very little light inside 

 a hive : but neither appears to me conclusive. 



I remember a little inaccuracy in the way I explained my 

 notion as to the manner in which bees are guided in making 

 their cells. I said that all the angles of the cell were of a cer- 

 tain type ; I should have said* all the trihedral angles. There 

 are of course three others, each bounded by four sides, but 

 these also have the fundamental property that all the dihedral 

 angles are of 120 degrees, so that the bee could always obtain 

 direct vision of the faces of each dihedral angle. 



Take two equal cubes, divide one into six pyramids, the base 

 of each being the face of the cube, and the apex at the centre of 

 the cube, fit each of the six pyramids by its base on a face of the 

 other cube, divide the solid thus got by a plane through the 

 centre of the central cube, normal to a diagonal. Each half is 

 the typical form of the bee's cell, except that the prismatic por- 

 tion of the latter is a little longer than according to this con- 

 struction it would be. There is of course no theory as to the 

 length of this portion of the cell, and I believe no accurate obser- 

 vations. 



The above is, I think, the simplest way of conceiving the 

 form of the cell, and as far as I know it is not given in any book: 

 it would certainly be the easiest way of modelling a cell. 



