Repetition of the same general plan of construction is certainly no mark of inferiority of original power, if accompanied by adaptations to new and further conditions. It is a proof that in one direction all the necessary power was used, and no more, and that in producing the distinct organisms the necessary amount of further power was also used. If we follow the resemblances of structure that may be traced through all the animals of a varied class, we shall find that they may be referred, as a rational and consistent hypothesis, to this method of giving to each animal its characteristic formation. If this is a rational hypothesis, it is so because it is consistent with all the observable phenomena; and consequently, the opposite hypothesis that all these phenomena of resemblances and differences are due to the law of evolution does not exclude every other explanation of their existence. To apply this now to one of the comparisons on which great stress is laid--the comparison between the brain of man and that of the ape. Two questions arise in this comparison: 1. Do the resemblances necessarily show that these two animals came from a common stock? 2. Do the resemblances necessarily show that man was descended from some ape through intermediate animals by gradual transformations? And, when I ask whether the comparison necessarily leads to these conclusions, I mean to ask whether the resemblances point so strongly to the conclusions that they must rationally be held to exclude every other hypothesis.