366 BPEOIAL INSTINOTS. 



having been taken from the spot on which it had teen 

 placed, and worked into the growing edges of the cells all 

 round. The work of construction seems to be a sort of 

 balance struck between many bees, all instinctively stand- 

 ing at the same relative distance from each other, all trying 

 to sweep equal spheres, and then building up, or leaving 

 ungnawed, the planes of intersection between these spheres. 

 It was really curious to note in cases of difficulty, as when 

 two pieces of comb met at an angle, how often the bees 

 would pull down and rebuild in different ways the same 

 cell, sometimes recurring to a shape which they had at first 

 rejected. 



When bees have a place on which they can stand in their 

 proper positions for working — for instance, on a slip of 

 wood, placed directly under the middle of a comb growing 

 downward, so that the comb has to be built over one face 

 of the slip — in this case the bees can lay the foundations of 

 one wall of a new hexagon, in its strictly proper place, 

 projecting beyond the other completed cells. It suffices 

 that the bees should be enabled to stand at their proper 

 relative distances from each other and from the walls of 

 the last completed cells, and then, by striking imaginary 

 spheres, they can build up a wall intermediate between two 

 adjoining spheres; but as far as 1 have seen, they never 

 gnaw away and finish ofE the angles of a cell till a large part 

 both of that cell and of tlie adjoining cells has been built. 

 This capacity in bees of laying down under certain circum- 

 stances a rough wall in its proper place between two just 

 commenced cells, is important, as it bears on a fact, which 

 seems at first subversive of the foregoing theory; namely, 

 that the cells on the extreme margin of wasp-combs are 

 sometimes strictly hexagonal; but I have not space here to 

 enter on this subject. Nor does there seem to me any 

 great difficulty in a single insect (as in the case of a queen- 

 wasp) making hexagonal cells, if she were to work alter- 

 nately on the inside and outside of two or three cells com- 

 menced at the same time, always standing at the proper 

 relative distance from the parts of the cells just begun, 

 sweeping spheres or cylinders, and building up interme- 

 diate planes. 



As natural selection acts only by the accumulation of 

 slight modifications of structure or instinct, each profitable 



