All enlightened schemes of physical culture and hygiene, although directed primarily to secure the strength, the health, and the happiness of the _present generation_, yet are sustained and ennobled by the conviction that the improvement of the individuals of each generation enters by inheritance into the gradual physical improvement of the race. All our schemes of education, intellectual and moral, though certainly intended mainly for the improvement of the individual, are glorified by the hope that the race also is thereby gradually elevated. It is true that these hopes are usually extravagant; it is true that the _whole_ improvement of one generation is not carried over by inheritance into the next; it is true, therefore, that we can not by education raise a lower race up to the plane of a higher in a few generations or even in a few centuries: but there must be at least a small residuum, be it ever so small, carried forward from each generation to the next, which, accumulating from age to age, determines the slow evolution of the race. Such are the hopes on which all noble efforts for race-improvement are founded. Are all these hopes baseless? They are so if Weismann and Wallace are right. If it be true that reason must direct the course of human progress, and if it be true also that selection of the fittest in the organic sense is the only method which can be used by reason, then the dreadful law of pitiless destruction of the weak, the helpless, the sick, the old, must with Spartan firmness be voluntarily and deliberately carried out. Against such a course we instinctively revolt with horror, because contrary to the law of our spiritual nature. But the use by reason of the Lamarckian factors is not attended with any such revolting consequences. All our hopes of race-improvement, therefore, are strictly conditioned on the efficacy of these factors--i. e., on the fact that useful changes, determined by education in each generation, are to some extent inherited and accumulated in the race. CHAPTER IV. SPECIAL PROOFS, TAKEN FROM THE GENERAL LAWS OF ANIMAL STRUCTURE, OR FROM COMPARISON IN THE TAXONOMIC SERIES. _General Principles._ =Analogy and Homology.=--In biology those organs or parts in different animals are said to be _analogous_ which, however different their origin, have a general similarity of form and especially of function; while those are called _homologous_ which, however different their general appearance, and however different their function, yet may, by close examination and extensive comparison, be shown to be modifications of one another--to be, in fact, originally the same part modified for different purposes. In the former the parts compared look and behave as if they were the same, but are not; in the latter they look and behave entirely differently, but are, in fact, the same part in disguise.