According to the now almost universally (that is, among educated scientific people) accepted theory of Evolution, each living being upon this earth is a result of a very slow process of development, which commenced with a low form of life many millions of years ago, and has since been operating continuously, becoming more and more complex, and imperceptibly attaining greater perfection as each fresh stage was accomplished. From the homogeneous to the heterogeneous, from inorganic to organic, from Amœba to man, the evolutionary development has slowly, steadily, and surely advanced step by step, in obedience to certain well-defined laws. Yet it is impossible to discern in this slow process of evolution any well-marked difference between one particular species and the next of kin, although the difference becomes clearly apparent if we take two species separated from each other by considerable time; just as it is impossible to detect any alteration in form and feature between a child of six days old and the same child of seven days old, while the change is very evident after the lapse of several weeks or months. If we were to photograph a human being regularly each day from the moment of its birth to the time of its decease at the age of eighty, we should be unable to detect any real difference between the portraits on any two consecutive days; but the difference between the child of a week old and the young man of twenty years would be enormous, as would be that between the full-grown youth and the tottering old man. As the human individual in its earliest condition of existence is not possessed of the same faculties as it afterwards enjoys as a more perfect development, so, in like manner, the species in its primal condition was wanting in the loftier qualities now possessed by the higher animals, such as consciousness, sight, hearing, taste, smell, and touch, all of which have been gradually evolved as the various life-forms developed from lower and more simple to higher and more complex kind. For instance, at a very early period of man’s individual existence he possessed no brain, eyes, ears, mouth, or nose, and, therefore, was quite incapable of mentating, seeing, hearing, tasting, or smelling; but, as the organism very gradually developed into a higher and more complex kind, these various organs manifested themselves, and slowly arrived at such perfection as we find in the human infant at birth. Precisely so was it with the race. The lowly Moneron was of homogeneous structure, possessing neither parts nor kind, but gradually differentiating into nucleus and cell; its descendants, the Gastrœada, becoming possessed, by a process of invagination, of an external layer of nucleated cells and an internal and more delicate layer, thus forming a hollow organism, or Gastrula. This external cellular integument was the original sense-organ of the animal kingdom, from which developed the organs of special sense.