90 THE BEGINNINGS OF IIFE. 



ticular ^ physiological units/ of which it is composed. 

 On this important subject Mr. Herbert Spencer says^: — 

 ^We must infer that a plant or animal of any species 

 is made up of special units, in all of which there 

 dwells the intrinsic aptitude 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. Groups 

 of units taken from an organism (providing they are 

 of a certain bulk and not much differentiated into 

 special structures) have this power of rearranging 

 themselves; and we are thus compelled to recognize 

 the tendency to assume the specific form as inherent 

 in all parts of the organism. Manifestly too, if we 

 are thus to interpret the reproduction of the organism 

 from one of its amorphous fragments, we must thus 

 interpret the reproduction of any minor portion of 

 an organism by the remainder. When in place of 

 its lost claw a lobster puts forth from the same spot 

 a cellular mass, which, while increasing in bulk, as- 

 sumes the form and structure of the original claw, 

 we can have no hesitation in ascribing this result to a 



have of arranging themselves into a special form," we may, with- 

 out assuming anything more than is proved, use the term "organic 

 polarity" or "polarity of the organic units" to signify the proximate 

 cause of the ability which organisms display of reproducing lost parts, 

 or of their having assumed the shape and structure which is peculiar 

 to them,' 



^ ' Principles of Biology,' 1864, vol. i. p. 181. 



