It is true that the gaps in the palæontological evidence, here as elsewhere, are many and keenly felt. In the order of the Primates they are greater than in many other orders, chiefly because of the arboreal life of our ancestors. The explanation is very simple. It is really due to a long chain of favourable coincidences if the skeleton of a vertebrate, covered as it was with flesh and skin, and containing still more perishable viscera, is petrified at all. The body may be devoured by other creatures, and its bones scattered about; or it rots away and crumbles to pieces. Many animals hide in thick undergrowth when death approaches them; and, leading an almost entirely arboreal life, the Primates are especially likely to disappear without being fossilized. It is only when the body is quickly covered with sand, or is embedded in suitable lime or silica containing mud, that the process of petrifaction can come to pass. Even then it is only by great good luck that we come across such a fossil. Very few countries have been searched systematically, and the areas that have been searched amount to little in comparison with the whole surface of the land, even if we leave out of account the fact that more than two-thirds of the globe are covered by water. These deplorable deficiencies of empirical palæontology are balanced on the other side by a growing number of positive facts, which possess an inestimable value in human phylogeny. The most interesting and most important of these is the celebrated fossil _Pithecanthropus erectus_, discovered in Java in 1894 by Dr. Eugène Dubois.[9] Three years ago this now famous ape-like man provoked an animated discussion at the third International Zoological Congress at Leyden. I may therefore be allowed to say a few words as to its scientific significance. Unfortunately, the fossil remains of this creature are very scanty: the skull-cap, a femur, and two teeth. It is obviously impossible to form from these scanty remains a complete and satisfactory reconstruction of this remarkable Pliocene Primate. [9] _Pithecanthropus erectus._ 'Eine menschenähnliche Uebergangsform aus Java' ('A Human-like Transitional Form'). Batavia, 1894.