18591863] BEES' CELLS. 121 



species would be fairly popular and have a fairly remunera- Letter 72 

 tive sale (which was the height of my ambition), for if it 

 prove a dead failure it would make me the more ridiculous. 



To W. H. Miller. 1 Letter 73 



Down, June 5th [[859]. 



I thank you much for your letter. Had I seen the 

 interest of my remark I would have made many more 

 measurements, though I did make several. I stated the facts 

 merely to give the general reader an idea of the thickness of 

 the walls. 2 



Especially if I had seen that the fact had any general 

 bearing, I should have stated that as far as I could measure, 

 the walls are by no means perfectly of the same thickness. 

 Also I should have stated that the chief difference is when 

 the thickness of walls of the upper part of the hexagon and 



1 William Hallowes Miller, F.R.S. (i 801-80), held the Chair of 

 Mineralogy at Cambridge from 1832 to 1880 (see "Obituary Notices 

 of Fellows," Proc. R. Soc., Vol. XXXI., 1881). He is referred to in the 

 Origin of Species (Ed. vi., p. 221) as having verified Darwin's state- 

 ment as to the structure of the comb made by Melipona domestica, 

 a Mexican species of bee. The cells of Melipona occupy an inter- 

 mediate position between the perfect cells of the hive-bee and the much 

 simpler ones of the humble-bee ; the comb consists " of cylindrical cells 

 in which the young are hatched, and, in addition, some large cells of wax 

 for holding honey. These latter cells are nearly spherical and of nearly 

 equal sizes, and are aggregated into an irregular mass. But the important 

 point to notice is that these cells are always made at that degree of 

 nearness to each other that they would have intersected or broken into 

 each other if the spheres had been completed ; but this is never per- 

 mitted, the bees building perfectly flat walls of wax between the spheres 

 which thus tend to intersect." It occurred to Darwin that certain 

 changes in the architecture of the Melipona comb would produce a 

 structure " as perfect as the comb of the hive-bee." He made a calcu- 

 lation, therefore, to show how this structural improvement might be 

 effected, and submitted the statement to Professor Miller. By a slight 

 modification of the instincts possessed by Melipona do?nestica, this bee 

 would be able to build with as much mathematical accuracy as the 

 hive-bee ; and by such modifications of instincts Darwin believed that 

 <c the hive-bee has acquired, through natural selection, her inimitable 

 architectural powers" (he. cit., p. 222). 



2 The walls of bees' cells : see Letter 173. 



