anthropoids much more closely than those of the lower monkeys. The foetus of the gibbon, figured by Selenka (Fig. 8), presents the most striking likeness to a corresponding human fœtus (Fig. 9).

Later on, the characters that distinguish man from even the highest of the apes become more and more pronounced. In the anthropoids the facial portion becomes more and more prominent, and betrays a bestiality absent from the human form. None the less the resemblance between the nearly mature fœtus of anthropoids and human embryos of about the sixth month is evident enough. M. Deniker had the good fortune to obtain the late foetus of a gorilla-a very rare piece of fortune--and he has made an elaborate investigation of its structure. The general appearance (Fig. 10) is quite enough to show the close relationship with a human fœtus of a corresponding age (Fig. 11). It is plain, moreover, that the young gorilla is more human-like than is the adult. Detailed anatomical investigation only confirms this conclusion.

The skulls of the young stages of anthropoids are much. more human in their character than the adult skulls. Selenka states that such young skulls of different anthropoids not only resemble one another more closely, but are more human. As soon as the teeth begin to appear, the individual characters are assumed so rapidly, and become so marked, that, in the absence of the intermediate stages, it would be difficult to establish the kinships.

The data derived from embryology do not point to any one of the existing genera of monkeys as the ancestor of man. They lead us to infer, rather, that man and the anthropoid apes had a common origin, and paleontological evidence must be scanned to find this ancestor. The greatest importance has been attached to a discovery in Java, made

in 1894 by Eugène Dubois. The remains, consisting of the crown of a skull, two teeth and a femur, belonging to a creature for which the name Pithecanthropus erectus* has been invented, have been interpreted by several anatomists as those of a form intermediate between man and the anthropoid apes. However, as the facts about this creature are meagre and have been interpreted differently, I shall not make use of them in my argument. Even apart from them, the simian origin of man may be taken as proved.

The series of facts that I have been employing as evidence of the relationship between men and anthropoid apes has been drawn from the observations of anatomists and embryologists. Darwin, seeking to broaden the basis of the argument, called attention to the resemblances of the parasites of men and apes, as evidence of a close similarity of physiological processes in the creatures. In the last few years, investigations in a very different field seem capable of throwing a novel light on the question.

When the blood of one mammal is injected into the body of another, the latter shows remarkable modifications. When there is added to a serum, prepared from the blood of a rabbit and consisting of a colourless transparent liquid, a few drops of blood drawn from another rodent (for instance a guinea-pig), nothing unusual happens. The blood of the guinea-pig preserves its normal colour, and its corpuscles remain practically unaltered. If, instead of adding guineapig's blood to the serum of rabbit's blood, we add a serum drawn from the blood of the guinea-pig, still no special change occurs.

If, however, a serum be prepared from the blood of a rabbit into which there had first been injected the blood

A summary of this question is to be found in a new volume by M. Alsberg, "Die Abstammung des Menschen," chap. iii., 1902.

D

of a guinea-pig, the serum shows new and striking qualities. The addition to it of some drops of guinea-pig's blood

FIG. 10.-Fœtus of gorilla (after Deniker). brings about, in a very short time, a changed appearance. The red liquid, at first opaque, becomes transparent.

The

mixture of the prepared serum of the rabbit with the blood of the guinea-pig will assume the colour of claret mixed

FIG. 11.-Human foetus of about five months.

with water. The change is due to solution of the red corpuscles of the guinea-pig in the blood-serum of the rabbit.

This serum has still another property not less worthy of attention. If there is added to it not pure blood but only blood serum of the guinea-pig, a disturbance in the mixture occurs almost at once, and leads to the forming of a precipitate more or less abundant.

The injection of the blood of the guinea-pig into a rabbit has therefore changed the serum of the latter by introducing new properties: that of dissolving the red corpuscles of the guinea-pig and of giving a precipitate with the blood serum of the same animal.

Frequently the blood serum of animals prepared by previous injections of the blood of other species of animals is strictly specific. In such cases the serum only gives a precipitate with the serum of the species which has furnished the blood for the injections, and only dissolves the red corpuscles of this same species. But there are some instances in which a serum of a prepared animal dissolves, not only the red corpuscles of the species which has furnished the injected blood, but those of allied species. Thus the blood serum of the rabbit, after some injections of blood of the chicken, becomes capable of dissolving not only the red corpuscles of the chicken but also those of the pigeon, although in a less degree.

It has been suggested that assistance could be rendered to forensic medicine by making use of this property of serums, to discover the origin of a certain blood. As is well known, it is often very important to decide whether a stain was caused by the blood of man or of another animal. Until quite recently it was not known how to distinguish human blood from that of other mammals. Experiments have been made to discover if the red corpuscles found in the blood stain could be dissolved by the serum of animals which had previously been injected with the blood of man.