It is true that in the tropics the white man has found it uncomfortable to work, and has often reduced the indigenes to a kind of slavery. But that either is inevitable and unavoidable because of the laws of social evolution, or any more than a temporary reversion, there is no reason for holding. Alfred Russel Wallace, who spent twelve years in the tropics, says in a recent article that the white man can and does work in every part of them. If he does not work, it is simply for the same reason that he does not work in Europe or the United States--namely, because he does not have to. When, however, necessity lays its heavy hands on him, driving him to earn his living by the sweat of his brow, he does it in the tropical region quite as well as he does in the temperate. That is shown particularly in Queensland. But when natives can be reduced to slavery the crime is committed with slight compunction, and defended on the same ground that it was defended in the South and elsewhere. The time must come, however, as it came in Brazil and in other countries where slave labor was found too wasteful and demoralizing, when it will be displaced with free labor. The time must come, too, when free institutions will be found as essential under the equator as farther north. Without them social evolution can not reach its highest point, nor man attain to his greatest happiness, a state that he is always seeking, no matter where he lives. Scientific Literature. SPECIAL BOOKS. The famous discovery in Java, by Dubois, of the skullcap, femur, and two teeth in the upper Tertiary rocks has led to many interesting discussions, among which was a paper read by Ernst Haeckel before the International Congress of Zoölogists, held in Cambridge, England, last year. In this paper Haeckel contended that in these remains we had at last the long-sought-for missing link.[A] This paper excited much interest, which led to a request for its publication. The intelligent public, without knowing much about the value of the osteological points under discussion, were ready to grant that here indeed was the missing link, since the highest authorities in science were divided in opinion as to whether the remains belonged to a very low member of the human race or a very high member of the manlike apes. The conclusion would naturally follow that it made but little difference whether the remains proved to be those of man or monkey, as here was a creature so intermediate in structure that it stood on the dividing line, so to speak. In this little book Haeckel presents the old evidences as to the structural similarities between man and the higher apes, and places the Java remains (_Pithicanthropus erectus_) as the last link in the chain of descent. He also traces the ancestors of the apes through the mammalian series down, step by step, to the lowest vertebrates, and on through the invertebrates to the lowest forms of life. The suggestions are in many cases hypothetical yet instructive,