278 Dynamic Theory. 



tendency of the operation of the agent in the case of any given organ- 

 ism is to build such organism as a crystal is built, putting each addi- 

 tional piece in the place required by the polarities of the parts already 

 placed. Considerable latitude is possible in doing this, as we shall 

 see, just as there is in the building of mineral crystals under apparently 

 uniform conditions. In any given locality where the conditions are not 

 subject to change, generation after generation is produced without much 

 variation, except toward the production of more perfect uniformity. 

 This is seen in the exact resemblance for each other shown by a herd of 

 buffalo, a flock of sheep, a drove of hogs, a flight of pigeons, a covey 

 of partridges, a hive of bees, . &c. Even in tribes and nationalities of 

 men this is shown. It is the same in plant life. Every individual be- 

 gins life as an organic crystal. Its polar points govern the energy" in 

 the disposition of its accretions. We have seen how some part of the 

 embryo goes ahead of the rest in fts development, as if it were in a fa- 

 vored position. But soon its growth is checked and another part is 

 brought forward. When the second part has reached a certain stage, 

 the first is free to go on again. Instead of being a single homogeneous 

 crystal, the organized body, composed of differentiated parts, appears 

 rather to be a combination of different sorts of crystals, each increasing 

 after a fashion of its own, and each, to a certain extent, influencing and 

 limiting the growth of the rest. 



Differentiation, in its more extended meaning, may include all the 

 variations made in the organism from the hereditary pattern, regard- 

 less of their cause. But what has been said already would seem to in- 

 dicate that although all the apparently different causes in reality fall 

 under one head they may, with -propriety, be placed in two sub-classes, 

 which are not, however, in strong contrast. One of these relates to the 

 larval or embryonic period of life in which the organism is passive ; the 

 other, to the condition in which the animal is active. In the former, 

 there are no reactions, or very simple ones, to complicate the direct 

 formative action of the polar energy in placing the new materials in 

 building the structure. In the latter, the reactions are so important and 

 prominent that they are apt to obscure the real force behind them. Be- 

 fore the birth of a mammal infant such variations as are made in its 

 structure are due to influences directly upon the mother. After the 

 birth, the differentiations are chiefly in consequence of peculiar condi- 

 tions in the environment, which cause peculiar modes of activity in the 

 animal itself. Before they can operate upon the animal, the various 

 forms of energy in the environment are all reduced to the polar energ} r , 

 appearing in nerve currents, muscle contractions, and glandular activ- 

 ities, so that, in reality, the same force operates at every period of exis- 

 tence. A good many examples of the effect of action in differentiating 



