in the human ovum, the aggregated mhi of cells out of which the creature is to arise, gives origin to a peripheral layer of cells, slightly differing from the rest which they include; and this layer subsequently divides into two???the inner, lying in contact with the included yelk, being called the mucous layer, and the outer, exposed to surrounding agencies, being called the serous layer: or, in the terms used by Prof. Huxley, in describing the development of the Hydrozoa???the endoderm and ectoderm. This primary division marks out a fundamental contrast of parts in the future organism. From the mucous layer, or endoderm, is developed the apparatus of nutrition; while from the serous layer, or ectoderm, is developed the apparatus of external action. Out of the one arise the organs by which food is prepared and absorbed, oxygen imbibed, and blood purified; while out of the other arise the nervous, muscular, and osseous systems, by the combined actions of which the movements of the body as a whole are effected. Though this is not a rigorously-correct distinction, seeing that some organs involve both of these primitive membranes, yet high authorities agree in stating it as abroad general distinction. Well, in the evolution of a society, we see aprimary differentiation of analogous kind, which similarly underlies the whole future structure. As already pointed out, the only manifest contrast of parts in primitive societies, is that between the governing and the governed. In the least organized tribes, the council of chiefs may be a body of men distinguished simply by greater courage or experience. in more organized tribes, the chief-clhi is definitely separated from the lower clhi, and often regarded as different in nature???sometimes as god-descended. And later, we find these two becoming respectively himen and slaves, or nobles and serfs. a glance at their respective functions, makes it obvious that the great divisions thus early formed, stand to each other in a relation similar to that in which the primary divisions of the embryo stand to each other. For, from its first appearance, the warrior-clhi, headed by chiefs, is that by which the external acts of the society are carried on:alike in war, in negotiation, and in migration. afterwards, while this upper clhi grows distinct from the lower, and at the same time becomes more and more exclusively regulative and defensive in its functions, alike in the persons of kings and subordinate rulers, priests, and soldiers; the inferior clhi becomes more and more exclusively occupied in providing the necessaries of life for the community at large. From the soil, with which it comes in most direct contact, the mhi of the people takes up, and prepares for use, the food and such rude articles of manufacture as are known; while the overlying mhi of superior men, maintained by the working population, deals with circumstances external to the community???circumstances with which, by position, it is more immediately concerned. Ceasing by-and-by to have any knowledge of, or power over, theconcerns of the society as a whole, the serf-clhi becomes devoted to theprocesses of alimentation; while the noble clhi, ceasing to take any part in the processes of alimentation, becomes devoted to the co-ordinated movements of the entire body-politic.

Equally remarkable is a further analogy of like kind. After the mucous and serous layers of the embryo have separated, there presently arises between the two a third, known to physiologists as the vascular layer???a layer out of which are developed the chief blood-vessels. The mucous layer absorbs .