VIII.] HOMOLOGIES. 199 



tlie symmetry ia undoubtedly the result of a "balance, 

 of forces," but to say so is a truism. The question is, What 

 is the cause of this "nutritional balancing?" It is here 

 contended that it must be due to an internal cause \vhich 

 at present science is utterly incompetent to explain. It is 

 an internal property possessed by each living organic whole 

 as well as by each non-living crystalline mass, and that there 

 is such internal power or tendency, which may be spoken of 

 as a " polarity," seems to be demonstrated by the instances 

 above given, which can easily be multiplied indefinitely. 

 ^Ir. Herbert Spencer '* (speaking of the reproduction, by 

 budding, of a Begonia-leaf) recognizes a power of the kind. 

 He says, " We have, therefore, no alternative but to say 

 that the living particles composing one of these fragments 

 have an imiate tendency to arrange themselves into the 

 shape of the organism to which they belong. We must in- 

 fer that a plant or animal of any species is made up of 

 special units, in all of which there dwells the intrinsic apti- 

 tude to aggregate into the form of that species ; just as, in 

 the atoms of a salt, there dwells the intrinsic aptitude to 

 crystallize in a particular way. It seems difficult to conceive 

 that this can be so ; but we see that it is so." .... " For 

 this property there is no fit term. If we accept the word 

 polarity as a name for the force by which inorganic units are 

 aggregated into a form peculiar to them, we may apply this 

 Avord to the analogous force displayed by organic limits." 



Dr. Jeffries Wyman," in his paper on the " Symmetry 

 and Homology of Limbs," has a distinct chapter on the 

 " Analogy between Symmetry and Polarity," illustrating it 

 by the effects of magnets on " particles in a polar con- 

 dition." 



35 "Principlos of Biology," vol. i., p. 180. 



3« Sec the " rrocccdings of the Boston Society of Natural History," 

 vol. xi., June 5, 1867. 



