112 HABIT AND INTELLIGENCE. [cHAP. 



the axes of the species. A form thus obtained, depending 

 on cleavage, is as truly a natural one as if it were obtained 

 simply by picking it up ; and it manifestly depends on 

 structure, of which cleavage is one of the most important 

 expressions. 

 Third The third kind of formative principle is that of vital 



producing Organization, to which the forms and structures of organisms 

 organisms, are due. The organic formative principles probably tran- 

 scend in complexity those which form crystals, almost 

 infinitely more than those which form crystals transcend 

 those which form spheres. Concerning the formation of 

 spheres there is no mystery whatever. Gravitation, and 

 every other primary force and ultimate projierty, are no 

 doubt inexplicable ; but, if we take the force as a datum, 

 it is self-evident that a force which is simply attractive 

 must tend to produce aggregations of spherical form. 

 Concerning the formative principles of crystallization we 

 know very little as yet ; but it does not appear beyond the 

 powers of man's intellect to find mathematical expressions 

 for the complex polarities that determine the characteristic 

 structure and form of every crystalline species, and even 

 Organiza- to discover their physical laws.^ But it never can be 

 pllcable'^" P^^ssible to give any mathematical statement, or any 

 physical explanation of those mysterious formative prin- 

 ciples in virtue of which the structureless and homo- 

 geneous germ of an organism acquires definite structure, 

 and separates into distinct organs. 



It needs no proof that in the case of spheres and 

 crystals the forms and the structures are the effect, 

 and not the cause, of the formative principles. Attrac- 

 tion, whether gravitative or capillary, produces the spherical 

 form : the spherical form does not produce attraction. 

 And crystalline polarities produce crystalline structure 

 and form : crystalline structure and form do not produce 

 crystalline polarities. 



^ See the chapter in Dana's Mineralogy on "Theoretical Crystallogeny. " 

 Also an article by the same author in the Philosophical Magazine, 

 September 1867, on the connexion between chemical constitution and 

 crystalline form. 



