202 ON THE ORIGIN OF SPECIES 



and planes, or even perceive when they are correctly 

 made. But the difficulty is not nearly so great as it at 

 first appears : all this beautiful work can be shown, 

 X think, to follow from a few very simple instincts. 



I was led to investigate this subject by Mr. Water- 

 house, who has shown that the form of the cell stands 

 in close relation to the presence of adjoining cells; and 

 the following view may, perhaps, be considered only as 

 a modification of his theory. Let us look to the great 

 principle of gradation, and see whether Nature does 

 not reveal to us her method of work. At one end of a 

 short series we have humble-bees, which use their old 

 cocoons to hold honey, sometimes adding to them short 

 tubes of wax, and likewise making separate and very 

 irregular rounded cells of wax. At the other end of 

 the series we have the cells of the hive-bee, placed in a 

 double layer : each cell, as is well - known, is an 

 hexagonal prism, with the basal edges of its six sides 

 bevelled so as to fit on to a pyramid, formed of three 

 rhombs. These rhombs have certain angles, and the 

 three which form the pyramidal base of a single cell on 

 one side of the comb, enter into the composition of the 

 bases of three adjoining cells on the opposite side. In 

 the series between the extreme perfection of the cells 

 of the hive-bee and the simplicity of those of the 

 humble-bee, we have the cells of the Mexican Melipona 

 domestica, carefully described and figured by Pierre 

 Huber. The Melipona itself is intermediate in struc- 

 ture between the hive and humble bee, but more nearly 

 related to the latter : it forms a nearly regular waxen 

 comb 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 com- 

 pleted ; but this is never permitted, the bees building 

 perfectly flat walls of wax between the spheres which 



