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ORGANIC EVOLUTION—PHYSICAL
in their ontogenies the evolution of their respective races, develop along parallel lines up to the point at which the races diverged, after which they develop along lines which are no longer parallel. It follows that the nearer the relationship between any two species, the longer does the course of the development from germ to adult proceed along parallel lines. Mr. Herbert Spencer puts the matter very clearly.
"The germ out of which a human being is evolved differs in no visible respect from the germ out of which every animal and plant is evolved. The first conspicuous structural change undergone by the human germ, is one characterizing the germs of animals only—differentiates them from the germs of plants. The next distinction established is a distinction exhibited by all Vertebrata; but never exhibited by Annulosa, Mollusca, or Coelenterata. Instead of continuing to resemble, as it now does, the rudiments of all fishes, reptiles, birds, and mammals; the rudiment of man assumes a structure that is seen only in the rudiments of mammals. Later, the embryo undergoes changes which exclude it from the group of implacental mammals; and prove that it belongs to the group of placental mammals. Later still, it grows unlike the embryos of those placental mammals distinguished as ungulate or hoofed; and continues to resemble the unguiculate or clawed. By and by, it ceases to be like any foetuses but those of the quadrumana; and eventually the foetuses of only the higher quadrumana are simulated. Lastly, at birth, the infant, belonging to whichever human race it may do, is structurally very much like the infant of all human races; and only afterwards acquires those various minor peculiarities of form that distinguish the variety of man to which it belongs."—Principles of Biology, vol. i. p. 142.
Following the above train of thought it may be remarked, that any trait which appears late in the
