454 HOMES WITHOUT HANDS. 



of rule and compass. Then, if the circles be not perfect, or their 

 centres wrongly placed, or the hollow of one cut deeper than that 

 ot another, or the hemispherical form of the hollow not precisely 

 just, the whole accuracy of the angles is destroyed, and the en- 

 tire comb would be as distorted as the first essays of a young 

 carpenter. 



Then there is another explanation, which may be called the 

 "equal pressure" theory. The Bee is, according to the advocates 

 of this theory, supposed to construct all the cells of a cylindrical 

 shape, and the cells are supposed to assume the hexagonal form 

 by equal pressure in all directions. Every one knows that cylin- 

 ders made of a yielding substance always become hexagonal if 

 pressed together, and a similar process was supposed to cause the 

 hexagonal shape of the bee-cell. 



There is another theory, which I believe to be entirely original, 

 which is suggested by the well-known mathematician and crystal- 

 lographer above mentioned. Mr. Mitchell writes to me as follows : 

 " It may not be out of place to remark that the bee-cell forms a 

 mould, as it were, of the natural form of a crystal. There ip in 

 nature a great variety of crystals, hexagonal prisms terminated 

 by three planes, like the bee-cell. These have many different 

 angles. But there is one form, called the rhombic dodecahedron 

 (Fig. 6), very frequently found in natural crystals of the garnet, 

 which has precisely the same angles as the bee-cell. 



" Certain crystals split naturally into planes precisely like the 

 lozenges which have already been described in giving the key to 

 the structure of the bee-cell. May it not, therefore, be possible 

 that wax, which is a crystalline substance, cleaves in this particu- 

 lar direction, and does the Bee use this property in forming its 

 cell ? Though this vague conjecture should prove to be true, we 

 shall not less admire the marvelous instinct which combines this 

 fact with the structure of the cell." 



It would, of course, be easy to fill many pages with the account 

 of the Hive-bee and its habits; but as this work is restricted to 

 the habitations of animals, we can only look upon the Bee as a 

 maker of social habitations. It will, however, be necessary to 

 mention the material of which the comb is made. 



The other hymenoptera, obtain their materials from external 

 sources. The hornet and wasp have recourse to trees and branch- 

 es, arid bear home in their mouths the bundles of woody fibres 

 which they have gnawed away. The upholsterer and leaf-cutter 



