ABSTRACT
In contriving the mechanisms of organic life, Nature, so prodigal in many respects, appears to favour the principle of economy. In the evolution of organic bodies, ideas are plentiful, but mechanisms few; rarely are old forms ruthlessly scrapped; new ideas and purposes generally mould new forms from older ones, the later arising through modifications of and additions to the earlier. No less does the principle of economy rule in the evolution of psychological structures and mechanisms.
