Lofty as is the human intellect at the present time, as compared with the mental powers of those we have left far behind in the march of evolution, it is yet very far from being able to grasp many of the great problems of the universe, such as that of existence. Perhaps at some future time, in millions of ages to come, these great questions may be answered; but at present we know they baffle the wisest men, and continually remind us of the finite and limited character of our intellectual faculties. This comparison of the mental development of the individual with that of the whole race is extremely interesting, and provides ample material for thought. By such comparison, and by it alone, can the science of psychology ever be based on a sure and enduring foundation. It is all very well for theologians and other biased people to declare that animal intelligence has nothing in common with the reasoning powers of man; but let them honestly look at the facts as they are, thanks to the indefatigable energy and indomitable perseverance of lovers of science and truth, now presented to us. Candid observers cannot fail to notice that the difference between the intelligence of man and that of the lower animals is one only of degree, and not of kind. When we see the order of sequence being followed in the development of the individual so like that of the whole race, not only as regards the bodily structure, but also as regards the mental functions, can we help arriving at the conclusion that the one is but the epitome of the other, and that the superior intellect of man is but a higher development of the so-called instincts of the lower animals? Have we not at the present day, among members of the human family itself, various degrees of intelligence, from the almost barren brains of the lowest races of savages to the brilliant mental achievements of a Newton or a Spencer?